This book constitutes the refereed proceedings of the 4th Hellenic Conference on Artificial Intelligence, SETN 2006, held at Heraklion, Crete, Greece in May 2006. The 43 revised full papers and extended abstracts of 34 revised short papers presented together with 2 invited contributions address many areas of artificial intelligence; particular fields of interest include: logic programming, knowledge-based systems, intelligent information retrieval, machine learning, neural nets, genetic algorithms, and more.