This book constitutes the refereed proceedings of the 19th International Conference on Principles and Practice of Multi-Agent Systems, PRIMA 2016, held in Phuket, Thailand, in August 22-26, 2016.The 16 revised full papers presented together with two invited papers, 9 short papers and three extended abstracts were carefully reviewed and selected from 50 submissions. The intention of the papers is to showcase research in several domains, ranging from foundations of agent theory and engineering aspects of agent systems, to emerging interdisciplinary areas of agent-based research.