Service-oriented architectures provide high levels of inter-operability and high means of adaptability. Nevertheless, distributed service-based business processes demand for robust, flexible and - bearing scalability in mind - efficient security mechanisms. This book presents access control models and procedures for intra- and inter-organizational service compositions. It introduces a framework for distributed access control in Web service federations and highlights optimizations through the consolidation of security policies and the caching of access control information. In combination, these concepts enable efficient and reliable access control for current and upcoming service-oriented architectures. As the presented techniques build up on prevalent security standards like WS-Security and XACML, application developers, system designers, and security experts will be able to seamlessly transfer them to their particular Web service-based projects.