This book constitutes the refereed proceedings of the 11th Portuguese Conference on Artificial Intelligence, EPIA 2003, held in Beja, Portugal in December 2003.The 29 revised full papers and 20 revised short papers presented were carefully reviewed and selected from a total of 119 submissions. In accordance with the five constituting workshops, the papers are organized in topical sections on artificial life and evolutionary algorithms, constraint and logic programming systems, extraction of knowledge from databases, multi-agent systems and AI for the Internet, and natural language processing...