This book constitutes the refereed proceedings of the 15th International Conference on Principles and Practice of Multi-Agent Systems, PRIMA 2012, held in Kuching, Sarawak, Malaysia, in September 2012. The conference was collocated with the 12th Pacific Rim International Conference on Artificial Intelligence, PRICAI. The 17 revised full papers presented were carefully reviewed and selected from 42 submissions. The papers are organized in topical sections on foundations, auctions and negotiation, coalition formation and teamwork, norms and institutions, and applications.