This book constitutes the thoroughly refereed post-proceedings of the 4th International Workshop on Agent-Mediated Electronic Commerce, AMEC 2002, held in Bologna, Italy in July 2002 during the AAMAS 2002 conference. The 20 revised full papers presented together with an introductory survey by the volume editors were carefully selected and improved during two rounds of reviewing and revision. The book gives a unique overview of the state of the art of designing mechanisms and systems for agent-mediated e-commerce- The papers are organized in topical sections on electronic auctions, negotiations, and electronic markets.