This book constitutes the refereed proceedings of the Third IFIP WG 11.11 International Conference, IFIPTM 2009, held in West Lafayette, IN, USA, in June 2009. The 17 revised full papers presented together with one invited paper and 5 demo descriptions were carefully reviewed and selected from 44 submissions. The papers are organized in topical sections on social aspects and usability, trust reasoning and processing, data security, enhancements to subjective logic, information sharing, risk assessment, and simulation of trust and reputation systems.