ThesearetheproceedingsoftheInternationalWorkshoponProgrammingMulti- Agent Systems (ProMAS 2008), the sixth of a series of workshops that is aimed at discussing and providing an overview of current state-of-the-art technology for programming multi-agent systems. The aim of the ProMAS workshop series is to promote research on progr- ming technologies and tools that can e?ectively contribute to the development and deployment of multi-agent systems. In particular, the workshop promotes the discussion and exchange of ideas concerning the techniques, concepts, - quirements, and principles that are important for establishing multi-agent p- gramming platforms that are useful in practice and have a theoretically sound basis. Topics addressed include but are not limited to the theory and app- cations of agent programming languages, the veri?cation and analysis of agent systems,aswellastheimplementationofsocialstructureinagent-basedsystems (e. g. ,roleswithin organizations,coordinationandcommunicationin multi-agent systems). In its previous editions, ProMAS constituted an invaluable occasion bringing together leading researchers from both academia and industry to discuss issues on the design of programming languages and tools for multi-agent systems. We were very pleased to be able to again present a range of high-quality papers at ProMAS 2008. After ?ve successful editions of the ProMAS workshop series, which took place during AAMAS 2003 (Melbourne, Australia), AAMAS 2004 (New York, USA), AAMAS 2005 (Utrecht, The Netherlands), AAMAS 2006 (Hakodate, Japan), and AAMAS 2007 (Honolulu, Hawai'i), the sixth edition took place on May 13 in Estoril, Portugal, in conjunction with AAMAS 2008, the main international conference on autonomous agents and MAS.