This volume constitutes the refereed proceedings of the Third Pacific Rim International Workshop on Multi-Agents, PRIMA 2000, held in Melbourne, Australia in August 2000 in conjunction with PRICAI 2000. The 13 revised full papers presented were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on coordination, negotiation, and learning; architecture, specificiation, and allocation; and applications in control and process management.