This book constitutes the thoroughly refereed post-conference proceedings of the 8th International Workshop on Engineering Multi-Agent Systems, EMAS 2020, held in Auckland, New Zealand, in May 2020. Due to the COVID-19 pandemic the conference was held virtually. The 10 revised full papers presented in this book were carefully selected and reviewed from 16 submissions. The papers cover a broad range of topics in the domains of agent-oriented software engineering, programming multi-agent systems, declarative agent languages and technologies, artificial intelligence, and machine learning.