This special issue consists of a collection of eight papers selected from the 2011 International Conference on Social informatics (SocInfo) that was held in Singapore from October 6 to 8. These are the journal versions of the best papers at the conference with significant newly added content. Each paper went through a separate multi-round peer review process for selection in the special issue. They together present a good range of social network analysis and mining topics.

The first paper “Modeling Wikipedia admin elections using multidimensional behavioral social networks” addresses the problem of modeling the election outcome of Wikipedia admin users using multidimensional behavioral social networks. The second paper “Endogenous control of DeGroot belief learning” proposes a extension of the DeGroot algorithm to derive social influence weights among a set of agents connected by a social network. The third paper, “Hypergraph index: an index for context-aware nearest neighbor query on social networks”, studies an efficient hypergraph index that supports context-aware nearest neighbor queries over social networks where the context can be defined by a set of keywords or the network structure. The fourth paper entitled “Robustness of social and web graphs to node removal” discovers the effect of different node removal strategies on the structure of social and web networks using efficient graph algorithms. The fifth paper “Online engagement factors on Facebook brand pages” determines the factors that increase online engagement of consumers using Facebook pages. Next, we have a paper “A mathematical model of dynamic social networks” that models the continuous evolution of a social network mathematically. This is followed by a paper that addresses crowdsourcing of human inputs to complex tasks by dividing the tasks into high quality and efficient subtasks. Finally, the paper “On the impact of text similarity functions on hashtag recommendations in microblogging environments” evaluates the different text similarity functions in hashtag recommendation.

The efforts of special issue preparation were by no means trivial. We must congratulate the authors of the above papers for finally getting their papers accepted in the special issue. We also thank the paper reviewers for recommending the papers and giving their valuable comments to improve the quality of the final set of papers. Finally, we thank the editor-in-chief, Reda Alhajj, for his useful guidance throughout the process.