The Portuguese Association for Artificial Intelligence has been organizing Portuguese Conferences on Artificial Intelligence, now held every second year, since 1985. This volume contains selected papers from the Fifth Conference on Artificial Intelligence. The conference has an international status: 62 contributions from 13 countries were received, of which 26 were from Portugal. To guarantee a high scientific standard, all the contributions were reviewed by at least three researchers,and only 20 papers were accepted and included in these proceedings. The papers are organized into sections on constraints, search, knowledge representation, temporal reasoning, planning, diagnosis and repair, and learning.