This special review series on non-alcoholic fatty liver disease (NAFLD) deals with the most recent and controversial issues related to NAFLD, which continues to increase worldwide and has emerged as a disease with high social burden. In addition, hepatocellular carcinoma associated with NAFLD has also increased, and the importance of NAFLD in future liver disease research is expected to increase gradually. Unfortunately, an effective treatment for NAFLD has not yet been developed; but as continuous clinical research is being conducted on candidate substances, we expect the development of an effective medication in the near future. A review series that will serve as the guideline for fatty liver research is absolutely necessary at this critical time.

The current issue consists of 26 reviews that contain a wide range of contents, such as updates on the latest knowledge and future research prospects for NAFLD, which would greatly help the readers to broaden their views on NAFLD and provide novel ideas for future studies. We tried to cover all aspects of NAFLD, including the definition, nomenclature, epidemiology, causes and comorbidities, screening, risk factors, non-invasive markers, high-risk population, surveillance, prevention and treatment, liver transplantation, and pathology. Of course, NAFLD-related research is developing rapidly, so there are many areas that we have not covered in this issue, and new research and concepts will be introduced soon. However, it would still be meaningful to compile the research results that are available so far.

We hope that this special review series on NAFLD will serve as an opportunity for all researchers and clinicians to resolve their queries and find the optimal answers related to NAFLD based on current literature. Above all, we would like to thank Professor Si Hyun Bae, the President of the Korean Association for the Study of the Liver, and the members of the Korean NAFLD Study Group for their financial and clerical support, as well as manuscript writing and research support. We also express our sincere gratitude to the current Editor-in-Chief of Clinical and Molecular Hepatology, Professor Seung Up Kim, who organized and published this special review series on NAFLD, along with the editorial board members and the distinguished scholars who contributed to the special review series.