This book constitutes the revised selected papers from the 12th International Workshop on Engineering Multi-Agent Systems, EMAS 2024, held in Auckland, New Zealand, during May 6-7, 2024. The 7 full papers and 4 short papers included in this book were carefully reviewed and selected from a total of 18 submissions. These papers focus on topics such as agent-oriented software engineering, programming multi-agent systems, declarative agent languages and technologies, artificial intelligence, and machine learning.