This book constitutes the refereed proceedings of the 12th International Conference on Artificial General Intelligence, AGI 2019, held in Shenzhen, China, in August 2019. The 16 full papers and 5 poster papers presented in this book were carefully reviewed and selected from 30 submissions. The papers are covering AGI architectures, discussing mathematical foundations, philosophical foundations, safety and ethics, and developing ideas from neuroscience and cognitive science.