This book presents the proceedings of the 4th International Conference on Trust, Privacy and Security in Digital Business (TrustBus 2007), held in Regensburg, Germany September 4–6, 2007. The conference continued from previous events held in Zaragoza (2004), Copenhagen (2005) and Krakow (2006), and maintained the aim of bringing together academic researchers and industry developers to discuss the state of the art in technology for establishing trust, privacy and security in digital business. We thank the attendees for coming to Regensburg to participate and debate the new emerging advances in this area.