How Does Retail Engage Consumers in Sustainable Consumption? A Systematic Literature Review

: The academic literature on consumer engagement and sustainable consumption has developed gradually over the last two decades. The body of knowledge related to the role of food and non-food retailers in this context, however, is only beginning to develop. The purpose of this systematic review is to analyse the existing literature on how retailers fulﬁl their role in engaging consumers in sustainable consumption. The need for a study with this purpose is proven by the fact that academic literature lacks a systematic review on this topic, despite the ascending trend in the number of published articles in the ﬁeld. This systematic review is based on a ﬁve-step process to ensure quality, replicability, transparency, and reliable conclusions. The reviewed articles were published relatively recently in academic journals from different domains. This review identiﬁed seven distinct types of retail marketing interventions (involvement of retailers in marketing actions with the aim to engage consumers in sustainable consumption), 30 types of retail marketing mechanisms (consisting in marketing strategies, techniques, tools, and channels used by retailers), and 14 distinct types of consumer engagement in sustainable consumption patterns. The review suggests an agenda for further research and identiﬁes practical implications for retail management.


Introduction
The emergence of the term sustainable consumption occurred during the Earth Summit of 1992 [1]. The research into sustainable consumption topics developed within the wider context of sustainability transitions, a research field that has evolved in the last 20-25 years [2]. A sustainability transition refers to a large-scale and long-term transformation of production and consumption systems. In this context, the aspects related to agency (the roles of firms and industries) were insufficiently addressed, particularly those related to food systems [3].
The research on sustainable consumption has evolved significantly from practiceoriented research focused on a single topic to the study of a range of inter-related topics (such as sustainability, consumption behaviour, energy utilisation, and environmental impact) [4]. Terminology-wise, the concept of sustainable consumption includes a contradiction between the terms "sustainable" and "consumption" [5]. The research literature is divided between a predominant weak approach (focused on the enhanced efficiency of consumption, mainly by means of technology) and a much-needed strong approach (centred on the changes in consumption levels and patterns) [6].
Researchers have discussed the "discursive struggles" to clarify the meaning of sustainable consumption, which have generated confusion among consumers and produced a "knowledge-to-action gap" in consumer behaviour [7]. Researchers have also identified and studied the "attitude-behaviour gap" that is reflected by the difference between attitudes towards sustainable consumption and actual purchase behaviours at retail stores [8][9][10][11].
Consumer engagement is considered an important concept for research in marketing and service management [28]. Two distinct streams have developed in this field [29]. The first considers the behavioural nature of customer engagement [30,31] and the second considers the psychological nature of customer engagement [32,33]. Researchers have focused primarily on consumer engagement in a virtual environment [34][35][36] and recently added an omnichannel perspective [37]. Nevertheless, specialists have identified a "lack of research" on the theoretical meaning of consumer engagement in sustainable consumption and its empirical relationship with other relevant constructs [31].
A distinct field of research encompasses the role of retail in influencing consumers towards sustainable purchases and consumption. The research in this field is evolving, with the number of published articles experiencing an ascending trend . Despite this evolution, the academic literature lacks systematic reviews on this specific subject, a fact that underlines the need for such a review.
The purpose of this review is to analyse the existing research literature on how retailers fulfil their role in engaging consumers in sustainable consumption. The research question is the following: "In what context and by means of what marketing strategies, techniques, tools and channels does retail engage consumers in sustainable consumption?".
The definition of the research question stems from the fact that consumer engagement is essential to support sustainable consumption and that retailers need to fulfil their role in engaging consumers in this direction. The buying and consumption decisions made by shoppers and consumers determine the content, intensity, directions, and costs of the flows of goods within the supply chains for consumer goods. Orientation towards sustainable consumption is not possible in the absence of rational and emotional support from the consumers' side. The expected change towards sustainable consumption patterns will become a reality only if the behaviours of consumers, not only their attitudes and stated intentions, consistently indicate such an orientation.
Retailers need to play an active role to engage consumers in this direction. A major reason for this role is the position held at the interface with shoppers and consumers in the distribution channels. The multifaceted role of retailers is related to the need to guide consumers through a sequence of stages leading to sustainable consumption. Thus, retailers must accompany consumers and shoppers during the following stages: becoming aware of the need to engage in sustainable consumption; development of favourable opinions relative to this approach; expressing preferences for sustainable products and sustainable consumption; sustainable purchase behaviour; sustainable consumption and waste reduction; becoming influencers who are able to encourage other persons to change their consumption patterns. To play such a role, retailers have a large range of tools at their disposal to engage consumers, such as product assortment, merchandising techniques, assistance provided by the store personnel, information available at point of sale, educational programs focused on such topics, etc. This systematic literature review had two major research objectives. The first objective is to obtain a descriptive perspective of the existing literature as reflected by the years of publication and the journal titles. The second objective is to obtain a thematic perspective that relies on the following categories: retail context, retail marketing intervention (involvement of retailers in marketing actions that aim to engage consumers in sustainable consumption), retail marketing mechanisms (including the marketing strategies, techniques, tools, and channels used by retailers to engage consumers), and consumer engagement in sustainable consumption.

Methodology
The elaboration of this article is founded on the requirements for high-quality literature reviews. According to Hart, the quality of a review relies on "appropriate breadth and depth, rigour and consistency, clarity and brevity, and effective analysis and synthesis" [61] (p. 1).
The approach presented in this article is specific to systematic literature reviews. For Petticrew and Roberts, such reviews "are a method for making sense of large bodies of information" [62] (p.2). Greenhalgh defines a systematic review as "an overview of primary studies, which contains a statement of objectives, sources and methods" and which "has been conducted in a way that is explicit, transparent and reproducible" [63] (p. 116).
By being systematic, such reviews meet the specific requirements of original empirical research [64] (p. 2). In comparison to other types of literature reviews, systematic reviews provide the advantage of limiting the bias in the identification and rejection of studies (due to the explicit method used), as well as the advantage of more reliable and accurate conclusions [63] (p. 118).
The academic literature underlines that systematic reviews must be elaborated according to a specific protocol that consists of several steps or tasks [61][62][63][64][65][66]. Following these requirements, the current systematic literature review was conducted in a sequence of five distinct steps: (1) Defining the purpose of the review, the research question, and the research objectives The purpose of this review was to analyse the existing literature on how retailers fulfil their role in engaging consumers in sustainable consumption. The research question was formulated as follows: "In what context and by means of what marketing strategies, techniques, tools, and channels does retail engage consumers in sustainable consumption?".
The systematic literature review aimed to achieve two main research objectives. The first was to develop a descriptive perspective of the existing literature, as reflected by the years of publication and the journal titles. The second was to obtain a thematic perspective that relies on the following categories: retail context, retail marketing interventions (involvement of retailers in actions that aim to engage consumers in sustainable consumption), retail marketing mechanisms (including the marketing strategies, techniques, tools, and channels used by retailers to engage consumers), and consumer engagement in sustainable consumption. The thematic categories were defined based on the logic suggested by Denyer, Tranfield, and van Aken for research synthesis [67].
(2) Identifying studies Based on the objectives of this review, several key search terms were defined and applied in the following string: (retail OR retailer OR store OR hypermarket OR supermarket) AND consumption AND (sustainable OR environmental OR green). The search was carried out during the period 10-13 February 2020. Using this search string, relevant studies were identified in four databases: Emerald Insight, Science Direct, Scopus, and Web of Science Core Collection. The selection of these databases was determined by the access they provide to high-quality and relevant literature.
This step of the review process led to a comprehensive list of documents for each searched database.
(3) Selecting and evaluating studies Several explicit criteria for the inclusion and exclusion of documents were defined and applied to ensure the transparent selection of studies from among the list of documents corresponding to each database. These criteria are highlighted in Table 1.
A total number of 45 articles remained after application of the selection criteria and the elimination of duplicates. An overview of the document selection is presented in Table 2.   No criteria were applied to further evaluate the quality of the remaining 45 articles.
(4) Analysing studies and engaging in synthesis Data extraction forms in electronic format were used to analyse the information present in the pool of articles and prepare a comprehensive summary. The information extracted from each article was registered in Excel worksheets according to the descriptive and thematic categories presented in Table 3.
In this step, the analysis and synthesis had an explanatory nature to underline the relationships between the categories applied to the thematic analysis of the reviewed articles. Based on explanatory logic, this review suggests that each retail marketing intervention is able to produce different forms of consumer engagement in sustainable consumption based on different types of marketing mechanisms applied by retailers in specific retail contexts.
(5) Reporting and using the results The results of the review process are presented in the next section of the article. This review facilitated the development of a research agenda, including suggestions for new directions of study. Several implications for retail management were also identified.
Diminishing bias was a priority during the design and implementation of the systematic review process. Compared to traditional approaches, this systematic literature review is replicable, scientific, and transparent, thus meeting the requirements underlined, among others, by Tranfield, Denyer, and Smart [68]. Several methods were applied to diminish bias, such as using the same key terms for the search in each database, engaging in a comprehensive search of relevant articles, and using explicit and reproducible criteria for article selection.

Results
This section presents the results of the systematic literature review. The analysis and synthesis of the selected articles revealed how retailers fulfil their role in engaging consumers in sustainable consumption.
This section of the article consists in two subsections that explore the results obtained in the review process, in accordance with the two major objectives. The first subsection is dedicated to the results corresponding to the first objective of the review, while the second subsection details the results related to the second objective.

Results Corresponding to the First Objective of the Review
The first objective of the systematic literature review was to obtain a descriptive perspective of the existing literature on how retailers fulfil their role in engaging consumers in sustainable consumption. The categories used for the descriptive analysis of the pool of articles were the year of publication and the journal title.
The distribution of articles by year of publication is shown in Table 4. The articles were published during the 2007-2019 period. In total, 82.22% of these articles were published between 2014 and 2019. This distribution reveals that the researchers focused on the reviewed topic relatively recently.
The distribution of the reviewed articles by journals is presented in Table 5. The articles selected for review were published in 27 distinct journals. Out of these, two titles (Journal of Retailing and Consumer Services; International Journal of Retail & Distribution Management) ranked first, holding a share of 20.00% of the total number of reviewed articles. The data from Table 5 also show that a significant share of journals (42.22%) only occasionally published articles on the topics addressed by this review. The journals that published the included articles are diverse in terms of their research domains. The journals dedicated to the retail domain were not the only ones that explored how retailers engage consumers in sustainable consumption. A wide array of journals include such articles. This situation was favourable for the development of this research topic, which was approached from multiple perspectives.

Results Corresponding to the Second Objective of the Review
The second major objective of this review was to obtain a thematic perspective of the existing literature on how retailers fulfil their role in engaging consumers in sustainable consumption. The analysis and synthesis of the information available in the relevant articles were based on the following categories: retail context, retail marketing intervention (involvement of retailers in actions that aim at engaging consumers in sustainable consumption), retail marketing mechanisms (including the marketing strategies, techniques, tools, and channels used by retailers to engage consumers), and consumer engagement in sustainable consumption.
The results obtained from this thematic perspective are presented hereafter for each of the above-mentioned categories that were analysed.

Results: Retail Context
The thematic analysis and synthesis of the information presented in the reviewed articles uncovered several categories of factors that define the retail context: type of product, country where the research was carried out, consumer profile, retail format, size of the retailer or store, shopping environment, and environmental issues.
One category of factors was related to the country where the research was carried out. The number of countries covered and the geographic areas differed between studies. Most articles were limited to one country. The rest of the articles considered/compared two or more countries: seven [38], five [54], four [41,73], and two countries [46,50,55,60].
The contextual factors also belong to the category of "consumer profile". The reviewed articles focused on either a large mass of consumers or only some groups and used different variables to define the profiles of consumers. Some of the articles reflected a large mass of consumers between 18 and 70 years old [38], shoppers aged 16-78 [43], consumers aged 18+ [90], or consumers that shop in malls [79]. Other articles considered specific groups of consumers, such as undergraduate students, university students [49,75], non-student adults from the Amazon Mechanical Turk [75], young adult consumers of fashion products aged 23-30 [44], women [74], women aged 65+ [82], consumers aged 20-49 [52], and children aged 7-10 along with their parents [51]. Membership to a loyalty program of a retailer was one of the variables defining the studied groups of consumers. Some researchers referred to loyalty card holders [40], while others focused on specific subgroups of consumers from among the large mass of shoppers that use the loyalty cards of a major supermarket chain [70] or on the long-term members of a loyalty reward program [80].
Another category of factors is related to the size of the retailer or store. The small retail size was exemplified by a butchery within a supermarket [45], an experimental food market within a supermarket [78], a specialist store in a shopping mall [79], and a small specialized green-product supermarket chain selling food and groceries [80]. Mediumsized supermarkets were also studied [48]. Many articles referred to operators of larger sizes like a major grocery retailer [64], the largest supermarket chain in the country [70], large supermarket chains [40,41], major supermarket chains [71], major retail chains with a significant market share [86], major supermarket retailers [46], food retail chains with the largest market share in terms of sales or number of stores [54], chain of more than 70 department stores [74], and the top 10 retailers in a country [83].
The contextual factors related to the shopping environment referred to "brick-andmortar" stores, online stores, and retail mock-up stores. Most research articles referred to an offline shopping environment, while other researchers focused on online retail [49] or explored both offline and online retail environments [58]. A retail mock-up store was, moreover, used for eye-tracking research [77].
The contextual factors also encompass environmental issues. Such examples include the high levels of clothing disposal and rapidly diminishing landfill space [79], as well as the fish species that are becoming endangered due to industrial-scale overfishing practices [46,89].
The categories of factors identified in the articles provide a diverse context for research that investigates how retailers fulfil their role in engaging consumers in sustainable consumption. However, the analysis revealed the tendency of researchers to investigate, to a greater extent, the contextual factors related to food products, European markets, supermarket formats, larger retail operators, and offline shopping environments.

Results: Marketing Interventions and Marketing Mechanisms for Consumer Engagement
Several types of marketing interventions were identified based on a thematic analysis and synthesis of the reviewed articles. Each type of marketing intervention consisted of a distinct action deployed by retailers to engage consumers in sustainable consumption. The main types of retail marketing interventions that were identified during the thematic analysis and synthesis were the following: providing sustainable choices for consumers; staging shopping experiences that enable consumers to make sustainable choices in store; editing choices in favour of sustainable consumption; reshaping norms to foster sustainable consumption; educating consumers about sustainable consumption; informing consumers about sustainability-related aspects; promoting sustainable shopping and consumption behaviour. Each type of marketing intervention was made possible via a marketing mechanism that consisted of specific strategies, techniques, tools, and channels. In this section, the types of marketing interventions and the corresponding marketing mechanisms for each marketing intervention are systematically presented.
Providing sustainable choices for consumers is a major type of retail marketing intervention to engage consumers in sustainable consumption. This marketing intervention consists of placing a range of goods and services, besides the conventional options, at the disposal of consumers to allow them to make sustainable choices. Several types of marketing mechanisms are able to support this type of marketing intervention through the following strategies: providing an assortment of products with different levels of sustainability; consistently ensuring the availability of sustainable products on store shelves; including self-made/private eco-brands of retailers in the store assortment; providing consumers with a range of sustainable services (e.g., recycling, reuse, repair, and rental) related to the tangible products.
Providing sustainable clothing options within the product assortment is a retail strategy aimed at encouraging more sustainable consumer behaviour [39].
The availability of sustainable apples and product variety in a store, for example, could be part of the mechanism that provides sustainable choices [40].
The strategy of offering an eco-friendly product assortment is also a way to increase the green premium applied by a retailer [77].
The eco-brands of retailers are a relevant way to connect with consumers who are preoccupied with environmental problems. These brands focus on underserved consumer niches related to health, product safety or superior food taste. They may complement the overall supply when the eco-brands of the manufactures do not meet the existing market demand either in terms of third-party certified eco-products or in terms of affordability [41].
The strategy of providing consumers with a range of sustainable services (e.g., recycling, reuse, repair, and rental) is relevant for sportswear-specialised retailers. By means of "re-projects", such a retailer can encourage consumers to donate their worn-out polyester clothes to be recycled into new garments, thus extending the product's life-cycle by means of repair services, to rent outdoor cloths instead of owning them, and to reuse products by buying second-hand items [72].
Retailers can combine several tools and communication channels (such as in-store magazines, e-newsletters, Facebook, websites, product stickers, and in-store demonstrations) to convey waste reduction messages [85].
Staging shopping experiences that enable consumers to make sustainable choices in store is another type of marketing intervention. This approach is represented by all the actions that create a shopping environment that is conducive to engaging consumers in sustainable choices. This marketing intervention relies on various types of marketing mechanisms, such as: a strategy to create a memorable shopping experience; techniques that create a store atmosphere and layouts that entice consumers to make sustainable product choices; merchandising techniques; the strategy of assigning sustainability ambassadors from one's own staff; the strategy of providing customer support via shop assistants who are knowledgeable about sustainability topics; the strategy of answering the questions about sustainability raised by shoppers in store; the technique of providing positive feedback to the shoppers who have made sustainable product choices in store.
These types of marketing mechanisms are presented in many of the reviewed articles.
Retail stores apply various strategies to influence consumers to engage in sustainable consumption behaviour [42], while adapting to the local understanding of sustainability and the local logic of sustainable consumption [86].
A technique able to create a store atmosphere that influences consumers to choose sustainable product alternatives consists of playing a sound from nature (such as a bird song) in a food retail setting [43].
The strategy of creating a memorable shopping experience must be centred on the consumer, especially in the case of sustainable fashion products [44].
Arranging green shopping trails is another technique applied to create a store atmosphere and a store layout able to stimulate consumers' sustainable choices. Such trails facilitate the identification of sustainable products by means of appropriate placement and signage in the store area [74].
The merchandising techniques that aim to increase the visibility of sustainable products in the store influence the shopping experience and enhance buying intentions. Consumers are often influenced by changing the size of the display area dedicated to sustainable products. Thus, consumers will engage in sustainable choices without deliberate thought [45]. In the case of plant-based protein items, common positioning is in the grocery aisles of supermarkets. Merchandising techniques used by stores to increase the value of plant-based protein item purchases include the following: augmentation of the number of product facings on shelves; locating plant-based meat substitutes away from meat to respond to the concerns of vegetarians and vegans; displaying plant-based protein items in the natural sections of the store, where price premiums are applied [71].
The store-related attributes that facilitate sustainable choices include customer service, store displays and environments, a store's ethical practices, and shop convenience [79].
Another retail strategy involves assigning sustainability ambassadors from among the staff in each store of a retail chain. Such ambassadors receive special training in sustainability and are responsible for training and informing the other staff members about sustainability topics [74].
A distinct strategy is based on shop assistants who are knowledgeable about sustainability topics and provide customer support consisting of specific sustainability information. These shop assistants are trained by special educational programs on sustainability issues and make use of IT systems for providing sustainability services to consumers [74].
Another strategy consists of answering the questions raised by consumers in stores. Shop assistants and customer service personnel answer questions related to the sustainable product range supplied by the store, the material content of the sustainable products, and the conditions under which these products were manufactured [74].
Another example of marketing mechanism is the provision of positive feedback to shoppers who make sustainable product choices in store. This technique aims to reassure shoppers and make them feel good about their choices "by putting green words in their bags" [74].
Editing choices in favour of sustainable consumption is a marketing intervention that has a corrective influence on existing consumption patterns, driving consumers towards more sustainable purchasing decisions. In contrast with other types of marketing interventions, editing existing choices has a disruptive effect, not a stimulating impact, on the habitual behaviours of shoppers and users. In this respect, retailers use various mechanisms such as the strategy of limiting choices of unsustainable products by delisting some of these products from their retail assortment; the strategy of reducing packaging related to shopping to a "package-free" level; a psychological interventional approach to reduce resource consumption (e.g., the use of plastic bags).
The strategy of limiting consumers' choices of unsustainable products could consist in providing alternative food choices alongside unsustainable products. For example, alternative fish species may be supplied alongside endangered cod species [46]. This strategy can also take the form of selling only sustainable labelled seafood [38]. Several food retailers have also stopped selling eel and giant tiger prawn [47].
Removing packaging as an artefact of shopping requires retailers to apply a strategy to reinvent the consumer practice of purchasing in stores. Package-free shopping entails practice reframing, the reskilling of shoppers, and changing store layouts [76].
The use of a psychological interventional approach to reduce resource consumption is based on a verbal prompt from the supermarket cashier that asks shoppers whether they want plastic bags [48].
Reshaping norms to foster sustainable consumption is a type of marketing intervention that involves actions aimed at transforming the attitudes and behaviours of consumers towards sustainable consumption. The effects can become visible in the long-term and potentially in the medium-term. The types of marketing mechanisms that support this marketing intervention are the strategy of developing descriptive norms and the strategy of shaping new ideal norms.
To encourage pro-environmental behaviour (e.g., the purchasing of green products), retailers can use realistic descriptive norm information about a minority behaviour [49]. The strategy of making reference to social norms in the marketing communication of retailers (e.g., "Join the millions of Italians that buy local" or "Join the Millions of Americans in Buying Local Produce") is a way to instil such norms related to sustainable consumption [50].
Retailers have a significant role in reshaping norms related to food consumption and in guiding that transformation process to new norms centred on transparency and the human scale, valuing food, enjoying real food as part of a good life, and intelligent and aware consumption. This role is founded on positive claims, reality tests (new interpretations of accepted norms), and denunciations [87].
Educating consumers in sustainable consumption is a necessary marketing intervention in the present state of consumer awareness, attitudes, and behaviours related to sustainable consumption. This type of marketing intervention consists in developing new and relevant knowledge and attitudes related to sustainable consumption among consumers. Examples of marketing mechanisms applied in such a marketing intervention include the strategy to establish partnerships between businesses and non-governmental organisations to accomplish educational objectives; the strategy to increase consumer awareness of environmental educational programs via green campaigns; the technique of using verbal information cues.
A strategy based on a partnership between a company and a non-governmental organisation was implemented between a major supermarket chain in Europe and the World Wide Fund for Nature. Aiming to educate consumers on sustainability topics, these organisations collaborated in the project "Animal Cards", through which shoppers were able to receive cards for every € 10 spent on groceries [51].
Educational videos shown in store provide another tool to increase consumer awareness of environmental topics [73].
Green campaigns based on environmental education programs (such as the "Environmental Camp for Children" and "Green Ladies and Gentlemen Campaign" for adults) can be run by a fashion retailer [52].
Educational programs of retailers can also use verbal information cues to orient shopper behaviour towards green products [81].
Informing consumers about sustainability-related aspects is a type of marketing intervention that develops the consumer's awareness and knowledge of product sustainability and sustainable consumption. Examples of marketing mechanisms applied to implement this marketing intervention include the following strategies: informing consumers about product sustainability; developing and using own responsible-choice label; using eco-labels on products with brands owned by the retailer; using environmental labelling schemes; using third-party certification labels; voluntary disclosure of sustainability information by retailers; providing sustainability information on the packages of products with organic logos.
An example of a retail strategy of informing consumers is the provision of transparent information on labour standards and material sourcing for fashion products [73]. Retailers also use brochures and magazines to provide consumers with information on food and climate [54]. Using digital displays and interactive screens, retailers communicate information on the origin and sustainability of products [56].
The strategy of retailers developing and using their own responsible-choice label allows consumers to identify products that meet the high environmental and social standards of the retailer [74]. The use of eco-labels on products with brands owned by the retailer is a strategy to shift demand towards lower-carbon products [70]. Researchers have studied the use of eco-labels for the promotion of the eco-friendly consumption of food [78].
The strategy of using environmental labelling schemes indicates that retailers have begun to inform consumers via carbon footprinting and carbon labelling [53]. For example, the green, yellow, and red colours of eco-labels indicate the sustainability and healthiness of fresh seafood products [89]. Nevertheless, retailers must explain the meaning of seafood eco-labels to consumers [55].
Retailers voluntarily disclose sustainability information using special labels with scale ratings that help consumers to assess the sustainability performance of the products [75].
The strategy of providing sustainability information on the packages of products with an organic logo focuses on promoting food production methods that can contribute to more sustainable agriculture [88].
Promoting sustainable shopping and consumption behaviour is a type of marketing intervention that encompasses a wide array of communication actions that encourage and motivate consumers to adopt positive attitudes towards sustainable consumption and engage in purchasing and consumption behaviours that support sustainability. Examples of the types of marketing mechanisms that contribute to this marketing intervention are the following: the strategy of positioning the retailer as a corporate brand focused on sustainability; the communication strategies and tools used to foster sustainable consumption behaviour; various types of marketing communication messages; the use of social media channels (e.g., Facebook and Instagram) for promotion.
The strategy of positioning the retailer as a corporate brand focused on sustainability consists of building an authentic image of an "eco-warrior" who is trustworthy and clearly committed to sustainability [58].
Communication strategies that foster sustainable consumption behaviour rely on the influence of opinion leaders and influencers such as bloggers [73]. One such public relations tool is the organisation of events for bloggers that cover sustainability topics [73]. An online newsletter is another public relations tool used by retailers to inform consumers about an online store [73].
Communication strategies using question-based verbal or written communication can be applied to influence consumer behaviour towards more environmentally friendly choices [59].
The promotion of an ethical lifestyle linked to moral motivations or healthy food consumption differs among the types of marketing communication messages that foster responsible consumption [73]. Emotions can play an important role in motivating people to change towards sustainable behaviour, but experts do not have a common viewpoint on the types of emotions (positive feelings of pride or negative feelings of guilt) that trigger responsible consumption [73]. Storytelling is a modern approach that is more effective in attracting consumers than assigning guilt [73]. Green claims (such as "ethical sourcing", "energy and water savings", and "cup recycling") are used, for example, to influence consumers' purchase intentions for coffee [57]. The positioning of the self-produced eco-brands of retailers is based on the products' relationship to market trends and lifestyles, as well as on the communication of personal benefits (e.g., health benefits) from the purchase of sustainable products [41]. Examples of pro-environmental claims include organic claims and carbon-neutral claims [60]. The range of advertising messages includes positive and negative appeals, with or without reference to the environment [82]. The retailers can communicate information on the sustainability-related attributes of products to influence consumer willingness to make value-differentiated choices [69]. Several retailers currently promote smarter food choices for the climate [47].
Social media are communication channels that help retailers not only to promote messages on sustainable consumption but also to obtain feedback from consumers [68]. Communication in social media is combined with retailer's reward programmes to boost green retail sales [79].
The present systematic literature review revealed that retailers can apply several types of marketing interventions to engage consumers in sustainable consumption. From a portfolio of goods, services, and brands to the shopping experience and from reshaping norms to educating and informing consumers, as well as promoting sustainable consumption, retailers are able to intervene using a relatively large range of marketing mechanisms.

Results: Consumer Engagement in Sustainable Consumption
The marketing intervention and marketing mechanisms applied by retailers can generate different types of consumer engagement in sustainable consumption. Nevertheless, research shows that sometimes retail marketing interventions and mechanisms do not succeed in engaging consumers.
The thematic analysis and synthesis of the reviewed articles identified the following types of consumer engagement: consumer awareness of sustainable products; green consciousness; consumer responsibility; consumer beliefs; consumer attitudes; psychological variables; purchasing intentions; consumer attention in store; willingness to buy and willingness to pay for green and organic products; choice of sustainable products in store; consumer purchase behaviour; sustainable consumption routines; packaging usage behaviour; consumer behaviour related to food waste.
One type of consumer engagement consists of consumer awareness of sustainable products. Staged experiences enable fashion consumers to acquire practical knowledge about sustainable fashion. In this way, consumers become more open to adopt the use of sustainable fashion products [44].
Researchers have identified consumer engagement under the form of green consciousness. The more favourable consumers' perceptions are of retailers' green products and green campaign activities, the greener the persons' consciousness and behaviour will become. Higher values perceived by consumers about products will thus have a more positive impact on encouraging consumers' eco-friendly behaviour [52]. In this way, retailers can influence consumers to be more environmentally conscious in their consumption. The influence of retailers mediates the relationship between concern for the environment and sustainable consumption [90]. The sustainability information provided through the digital displays in a store influences consumers to think more about environmental concerns [56].
Retail actions can augment consumer responsibility related to sustainable consumption. In the fashion sector, retail intervention enhances the responsibility of consumers and makes them want to change their own shopping behaviour [73].
On-package information can help to develop favourable consumer beliefs. In the case of food products, information related to production standards on a package is favourably perceived by consumers. The combined presentation of both an organic logo and information has a greater effect on consumers' beliefs about the product than an organic logo alone. Consumers consider such products to be more animal friendly, better for nature and the environment, and healthier than the ones with just the logo. However, a product with both a logo and details was considered to be more expensive, although the prices were actually similar [88]. Providing more detailed attribute information improves consumers' beliefs about the quality of a green product [81].
Consumer engagement can have a positive influence on consumer attitudes. Social norm messaging can, for example, positively influence consumers who are not inclined to purchase food locally. The effectiveness of messages increases with an unfavourable attitude towards local buying [50]. Many consumers have a positive attitude towards the use of carbon labels on food products and consider them to be useful to compare the environmental credentials of different food products [53].
Consumer engagement can be identified at the level of several psychological variables. Green claims develop a green image for the retailer's brand and have a positive impact on green psychological variables such as green trust, green satisfaction, green brand equity, and green purchase intentions. The claim of employing "ethical sourcing" has a greater impact on such variables than the claims of employing "energy and water savings" and "cup recycling" [57].
Another type of consumer engagement relates to purchasing intentions, which are positively influenced by the actions of retailers. There is research evidence that verbal information (in contrast to numerical information) has a positive influence on the purchase intentions for green products [81]. Other findings revealed that both rational and emotional advertisements with environmental messages targeting elderly female consumers more strongly encouraged purchase intentions for environmentally sustainable apparel than advertisements with no environmental messages [82].
Consumer engagement may take the form of consumer attention in store, which can be positively influenced by retailers. Research findings show that the use of a green colour has a strong influence on a consumer's visual attention because this colour tends to indicate organic and natural characteristics [77].
Another type of consumer engagement refers to the willingness to buy and willingness to pay for green and organic products. Playing nature sounds in a store has a direct and positive influence on the willingness to buy organic foods among groups of customers (men) that have relatively low initial intentions to buy [43]. The amount of money a consumer would pay for a green product increases when more detailed information on that product is provided, thus reducing the barrier to purchase [81]. The use of a retail mechanism to make consumers look longer at eco-friendly products positively influences the shopper to pay a higher green premium [77].
Consumer engagement also refers to the choice of sustainable products in store. Communication strategies that involve influencing consumers with a question increase the choices of environmentally friendly offerings compared with non-environmentally friendly alternatives. Verbal questions addressed by a store employee are more effective in influencing consumer behaviour than written forms of communication such as a written sign [59]. Visual cues can also create a shift in consumer purchasing behaviour, leading to sustainable meat choices. The sales of these products increase when the size of the display area and the quantity of the displayed products are increased [45]. The detailed information provided on a package also enables consumers to choose more in accordance with their personal values [88]. The presentation of full information on all sustainability-related attributes of a product influences consumers to make price/benefit trade-offs, resulting in the selection of higher priced, more value-differentiated products. If a retailer provides sustainabilityrelated information for some products and not for others, consumers will not purchase the non-sustainable option [69].
The marketing interventions of retailers can lead to a major type of engagement that influences consumer purchase behaviour. There is a positive relationship between social media posts (communicating messages relative to health, environmental benefits, and price) and green retail purchases made by longer-term members of loyalty reward programs. The impact of green product social media posts was shown to be stronger for customers who are long-term members of the loyalty rewards program of a given retailer [79]. In comparison to a default label, the use of easy-to-interpret but comprehensive environmental information label increases the overall purchases of eco-friendly food products [78]. Findings suggest that consumers' likelihood to buy sustainable seafood increases when the meaning behind the certification of such products is explained. However, it is not clear if consumers resonate with eco-labels [55]. The store-related attributes also positively influenced the eco-fashion consumption decisions of consumers. Nevertheless, the premium level of eco-fashion price negatively moderated this relationship [79]. The availability and variety of sustainable apples in stores positively influenced purchasing behaviour [40]. Reference to descriptive norms is also an effective incentive tool for the online shopping of green products. Consumers presented such norms were willing to add, on average, one eco-product to their grocery basket and spend 10% more money [49].
Retailers positively influence consumption by consolidating sustainable consumption routines. Easy-to-follow sustainable consumption cues provided by retailers (e.g., eco-labels and brands, product origin, various dietary ingredients, and seasonality), high visibility of products, and in-store marketing actions reinforce established sustainable consumption routines [42].
Another type of consumer engagement is related to packaging usage behaviour. The retailer's intervention can lead to package-free shopping. However, this result is possible only by reinventing shopping practices [76]. Moreover, the voice prompt of a cashier can lead to pro-environmental changes in behaviour, materialised as the decreased usage of plastic bags. This mechanism relies on discouraging unintentional usage and encouraging an intentional reduction in usage [48].
Consumer behaviour related to food waste complements the list of consumer engagement types. Retailers can positively influence consumer behaviour towards food waste reduction. Combined communication channels and repeated messages over time have a significant effect in this respect [85].
Besides the above-mentioned types of consumer engagement in sustainable consumption, there is evidence that retailers sometimes do not succeed in engaging consumers. Such examples of unfulfilled roles are reflected by the following outcomes: scepticism about a retailer's intervention; sales decline; undermining sustainable consumption; negative impacts on perceptions, buying intentions, and purchasing behaviour.
There is also the problem of scepticism among consumers. Some people expressed doubts that large mainstream retailers can be sustainable and "natural". According to these individuals, green retailers are of a small scale [74].
Retail interventions aiming to engage consumers in sustainable consumption sometimes led to the negative outcome of a sales decline. Choice editing led to overall sales losses because shoppers were not provided with the desired level of access to low-price products [46]. Research findings have shown that information provided about the sustainability and healthiness of fresh seafood products lead to an overall statistically significant decline in seafood sales, determined especially by a decline in the sales of "yellow"-labelled seafood products (yellow means a "good alternative", as the species come from fisheries or farms with good quantities, but some environmental concerns still exist). No statistically significant difference in the sales of green ("best choice") or red ("worst choice") labelled seafood has been identified [89].
Some types of mechanisms undermined sustainable consumption. Cross-sector partnerships focused on educational programs had the potential to improve environmental awareness among consumers. However, programs based on "animal cards" encouraged card collection and product purchases, thus undermining responsible and sustainable consumption [51].
The actions of retailers sometimes generated a negative impact on perceptions, buying intentions, and purchasing behaviour. Few consumers thought that carbon footprint labels on products indicate better food quality. Moreover, most consumers agreed or strongly agreed that understanding carbon footprint information and comparing carbon footprints are difficult and confusing tasks [53]. The effect of the presentation of a large number (e.g., six) of numerical cues negatively influenced purchase intentions [81]. Price was shown to have a strong and negative influence on consumer's purchase behaviour for sustainable apples [40]. In another study, the strategy of a retailer to sell only sustainable seafood and increase prices by more than 8% made shoppers switch to another store [38].
For each retail marketing intervention, the actual engagement of consumers in sustainable consumption depends on the choices made by the retailer in terms of marketing strategies, techniques, tools, and channels. The types of retail marketing intervention and mechanism must be applied after an evaluation of the potential results in terms of consumer engagement in sustainable consumption.

Discussion
The purpose of this review was to analyse the existing literature on how retailers fulfil their role in engaging consumers in sustainable consumption. The research question was the following: "In what context and by what marketing strategies, techniques, tools, and channels does retail engage consumers in sustainable consumption?". The findings of this systematic literature review led to several discussion points, which are presented below.
The first point refers to the existence of similar ascending trends in research and business with regard to the engagement of consumers in sustainable consumption. Both the academic and business communities show increasing interest in this topic. The scientific literature reveals that scholars are devoting ever-greater attention to studying how retailers engage consumers in sustainable consumption. Thus, the academic research is in line with the emerging business practice focused on enhancing sustainable consumption. The different types of marketing interventions and marketing mechanisms applied by retailers to engage consumers in sustainable consumption are an integral part of a new trend in the practices of companies involving business-led sustainable consumption initiatives [91].
The second discussion point focuses on the growing interest shown by scholars and practitioners in the role of retailers as a new paradigm for thinking about the responsibilities to ensure sustainable consumption within the wider framework of the debate on sustainability topics. The role of developing sustainable consumption cannot be assigned to consumers only, making them responsible for putting pressure on producers and retailers to orient them towards sustainable production and offering [92]. Retailers must also play a major role due to their position in the supply chain at the interface with shoppers and consumers.
The third discussion point underlines the current development stage of the academic literature. The number of articles that were the object of this systematic literature review demonstrates that research literature on this topic is only at the beginning of its growth stage. The research on how retailers fulfil their role in engaging consumers in sustainable consumption has real development potential in the near future, in parallel with the increasing interest of researchers and practitioners in the wider domain of sustainable consumption.
The fourth discussion point relates to the available knowledge on the potential types of retail marketing interventions and mechanisms for consumer engagement. The findings of this review demonstrate that retailers can select from a relatively wide range of different types of marketing interventions and marketing mechanisms to fulfil their role in engaging consumers in sustainable consumption. The intermediary position held by retailers in the supply chains between producers/manufacturers and consumers will help retailers to drive sustainable consumption.
Ultimately, another discussion point underlines the consumer engagement stages explored by the relevant research. The definition of the sustainable consumption process encompasses three distinct stages-the acquisition, usage, and disposal of goods and services [93]. According to this systematic review, the different types of consumer engagement practices determined by the retail intervention and mechanism relate predominantly to the purchasing (acquisition) stage. The reviewed articles did not focus, as their main research topics, on the stages involved in the usage and disposal of goods for the marketing interventions of retailers.

Conclusions
This systematic literature review aimed to analyse the existing literature on how retailers fulfil their role in engaging consumers in sustainable consumption. The decision to conduct a review of a systematic nature was based on the need to ensure an appropriate level of quality, transparency, and reproducibility, as well as to generate reliable conclusions.
This systematic literature review has some limitations. Only articles published in scientific peer-reviewed journals were considered, while other types of published documents were excluded. The reason for this selection was to ensure the inclusion of relevant research that reached the stage of publication in such journals. The articles published after the completion of the database search were also not considered for the review. Four databases were searched: Emerald Insight, Science Direct, Scopus, and Web of Science Core Collection. These databases were selected because they hold leading positions in terms of the high-quality and peer-reviewed journals they index and the abstracts or to which they provide access.
More than 80% of the 45 articles that were selected after the application of clearly specified inclusion and exclusion criteria were published from 2014 onwards. This fact shows that research on how retailers fulfil their role in engaging consumers in sustainable consumption is relatively recent and that development opportunities exist.
The articles were published in journals focused on various research domains, including retailing, distribution, production, business research, business, food products, fashion, etc. The multidisciplinary nature of this topic adds further value to the applied research approach.
The thematic analysis of the reviewed articles was based on the following four categories: retail context, retail marketing interventions (the involvement of retailers in marketing actions that aim to engage consumers in sustainable consumption), retail marketing mechanisms (marketing strategies, techniques, tools, and channels used by retailers to engage consumers in sustainable consumption), and consumer engagement in sustainable consumption. The relationship between these categories can help explain how retailers fulfil their role in engaging consumers in sustainable consumption. Indeed, each retail marketing intervention has the potential to generate different forms of consumer engagement in sustainable consumption on the basis of the retail mechanism applied in a specific retail context.
The review results indicated the retail contexts in which the retail marketing interventions and retail marketing mechanisms for consumer engagement are applied. The analysis and synthesis of the reviewed articles uncovered the tendency for researchers to study, to a greater extent, the retail context factors that are related to food products, European markets, supermarket formats, large retail operators, and offline shopping environments. These results reveal the need for further studies in more diverse contexts, including different food and non-food product categories, markets from geographical areas other than Europe, retail formats and operators of different sizes, and online stores/marketplaces. This systematic literature review identified several types of retail marketing interventions, retail marketing mechanisms, and types of consumer engagement in sustainable consumption, which are summarised in Appendix A.
The findings of this systematic literature review will facilitate the identification of new directions of study for the future research agenda, which is presented hereafter.
The main directions suggested for the future research agenda relate to the following aspects: concept of retailer's role in engaging consumers in sustainable consumption, application of the service and systems approach, stages of the engagement process, product categories, omnichannel perspective, drivers of the involvement of retailers in engaging consumers in sustainable consumption, influencing factors and moderating factors, and measurement of the consumer response to the engagement actions of retailers.
The concept of retailer's role in engaging consumers in sustainable consumption must be clarified. Lately, a significant body of academic literature has addressed the consumer engagement, but mainly in relation to social media and brands, not in relation to retailer involvement in engaging consumers in sustainable consumption.
Another direction of future research should address the need for a paradigmatic change in the retail marketing thinking relative to consumer engagement in sustainable consumption. This transformation should involve the application of the service and systems approach to retail marketing [94]. Scholars must integrate the interactions and relationships between retailers and consumers, as well as value co-creation, in the service and systems approach.
The stages of the engagement process are another potential direction of research. The stage consisting in the creation of consumer awareness and knowledge related to sustainable consumption should be studied alongside the stages of acquisition, use, and disposal.
As regards the product categories, to date, mostly food products and fashion/clothing products have been investigated. Further research should consider the consumer's engagement in the sustainable usage of non-food products such as electronics, household appliances, and furniture.
A distinct direction of research could study the role of retailers in engaging consumers that have omnichannel behaviour based on the joint use of conventional and online stores alongside traditional and social media channels.
Another research direction could identify the drivers of the involvement of retailers in engaging consumers in sustainable consumption. An in-depth analysis is required to identify the existence of other drivers besides profitability, environmental policy, and stakeholder pressure.
An important direction of research consists of the identification and study of the various influencing and moderating factors. There is a need for information on the factors that influence the level of consumer engagement, the factors that determine the duration of consumer engagement in sustainable consumption, and the factors that moderate the relationship between the marketing mechanism chosen by the retailer and the level of consumer engagement.
A major direction of research consists in understanding and measuring consumer response to each type of engagement intervention and mechanism applied by retailers. There is a need to measure the reactions of consumers to information and promotion campaigns for sustainable consumption, as well as to new store experiences and new norms.
The findings of this systematic review have direct implications for retail management. Retail operators must balance two distinct decision areas related to their environmental impact-corporate environmental sustainability and the engagement of consumers in sustainable consumption. At present, the sustainability agendas of retailers are dominated by strategies and measures aiming mostly at conserving energy, reducing greenhouse gas emissions, and sometimes recycling packaging materials and reducing waste. In the future, the societal expectations of retailers will be higher in terms of their expected contributions to the promotion of sustainable consumption.
A direct implication of retail management consists in measuring additional key performance indicators. The measurement of successful performance could integrate metrics assessing the contributions of retailers to the promotion of sustainable consumption among consumers besides metrics that are focused on profitability.
Retailers must disseminate specialised knowledge among all their employees, especially among the frontline employees. Periodic training programs are, therefore, necessary. Retailers can assign "sustainability ambassadors" responsibilities for the diffusion of sustainability knowledge among store employees. Another priority for retailers could be to enhance the customer-driven abilities of vendors and customer care employees to provide customer information on sustainable consumption topics.
Another direct implication for retail management is the need to involve consumers in the crowdsourcing of ideas able to generate positive shifts towards sustainable consumption patterns. Retailers must develop new programs for the promotion of sustainable consumption in direct collaboration with consumers. The involvement of consumers in designing product and service offerings, store experiences, and information and communication campaigns focused on sustainable consumption could introduce innovative ideas and increase the likelihood of achieving a high impact.
The academic literature on how retailers engage consumers in sustainable consumption is only at the beginning of its growth stage. In-depth studies are thus necessary to answer ten crucial research questions: • What is the most accurate definition of a retailer's role in engaging consumers in sustainable consumption? • How can systems thinking contribute to the identification of effective ways to engage consumers in sustainable consumption? • What stages of the consumer engagement process are most critical to successful involvement in sustainable consumption? • What would be the most reliable retail marketing mechanisms that are able to engage consumers in the sustainable consumption of specific product categories?
• How could retailers design a seamless omnichannel experience that is able to successfully engage consumers in sustainable consumption over the long-term? • What marketing drivers can generate the highest level of retail involvement in engaging consumers with sustainable consumption? • What factors influence the level of consumer engagement? • What factors determine the duration of consumer engagement in sustainable consumption as a result of the retail marketing mechanism? • What factors moderate the relationship between the marketing mechanism chosen by the retailer and the level of consumer engagement? • What, and how, should retail marketers measure to evaluate the level of consumer engagement in sustainable consumption and the effectiveness of the retail approach?
These research questions reveal the need for reliable and valid answers, as well as the numerous opportunities for further studies.
Funding: This research received no external funding.

Conflicts of Interest:
The author declares no conflict of interest.
Appendix A Table A1. Types of retail marketing interventions, retail marketing mechanisms, and consumer engagement in sustainable consumption.

Retail Marketing Interventions Retail Marketing Mechanisms Consumer Engagement in Sustainable Consumption
Providing sustainable choices for consumers • Providing an assortment of products with different levels of sustainability • Creating a store atmosphere and store layout enticing consumers to make sustainable product choices  • Using social media channels (e.g., Facebook, Instagram) for promotion