Environmental and social crises in agriculture have led to growing recognition that more ecologically sustainable and socially just food and agricultural systems are needed. This thematic number of the International Journal of Agriculture and Natural Resources gathers the papers submitted to the workshop “Challenges for agroecology development for the building of sustainable agri-food systems,” an OECD Co-operative Research Programme-sponsored conference. The aim of the workshop was to promote the transition from conventional agriculture towards agroecology as a science, practice and social movement through sharing the experiences of different OECD countries: Australia, Canada, Chile, Colombia, Hungary, Italy, Netherlands, Norway, Spain, Sweden and the United States. The main topics discussed at the workshop included i) agroecology development in OECD countries: local experiences and international collaboration; ii) agroecology as a social movement and related public policies; iii) agroecology education to promote sustainable agri-food systems; and iv) science, innovation and technologies in agroecological systems. While not a comprehensive assessment of the state of agroecology in OECD countries, this thematic number integrates diverse perspectives on some main research and policy advances and uncovers some existing gaps in agroecology practice as an approach for transitioning towards ecologically sustainable and socially just agricultural systems.