This book constitutes the thoroughly refereed post-conference proceedings of the Third International ICST Conference on Security and Privacy in Mobile Information and Communication Systems (MOBISEC 2011) held in Aalborg, Denmark, in May 2011. The 15 revised full papers were carefully selected from numerous submissions and cover the most active areas of research in mobile security with its 3 focus areas machine-to-machine communication security, policies for mobile environments, and mobile user authentication and authorization.