The volume aims at providing a comprehensive review of the diverse efforts covering the gap existing between the two main perspectives on the topic of ontologies for multi-agent systems. On the one hand, there is the knowledge modelling perspective; i.e. how ontologies should be modelled and represented in order to be effectively used in agent systems. On the other hand, there is the agent perspective; what kind of capabilities should be exhibited by an agent in order to make use of ontological knowledge and to perform efficient reasoning with it. Theory and experiences are emphasized as the volume collects the most significant papers of the AAMAS 2002 and AAMAS 2003 workshop on ontologies for agent systems, and the EKAW 2002 workshop on ontologies for multi-agent systems.