This book constitutes the thoroughly refereed post-proceedings of the 7th International Workshop on Agent-Mediated Electronic Commerce, AMEC VII 2005, held in Utrecht, Netherlands in July 2005, as part of AAMAS 2005, and the third Workshop on Trading Agent Design and Analysis, TADA 2005, held in Edinburgh, UK in August 2005, in the course of the IJCAI 2005 conference meetings. The seven revised full AMEC 2005 papers presented were carefully selected.