This book constitutes the proceedings of the the 11th Pacific Rim International Conference on Multi-Agents, PRIMA 2008, held in Hanoi, Vietnam, in December 2008. The 19 regular papers and 22 short papers presented together with 3 keynote speeches, were carefully reviewed and selected from 56 submissions. Many current subjects in multi-agent research and development are addressed, ranging from theoretical and methodological issues to various applications in different fields. There was a track on multi-issue negotiation and agents and HCI.