This volume constitutes the proceedings of the 4th International Conference on Trust Management, held in Pisa, Italy during 16-19 May 2006. The conference followed successful International Conferences in Crete in 2003, Oxford in 2004 and Paris in 2005. The ?rst three conferences were organized by iTrust, which was a working group funded as a thematic network by the Future and Emerging Technologies(FET) unit of the Information Society Technologies(IST)...