This book focuses on the access control problems in network-based systems and web-based scenarios. It illustrates basic principles and traditional solutions as well as advanced topics such as digital identity management, credential-based access control and trust management, and P2P systems. Besides presenting the concepts, the book gives practical guidelines for designing secure applications in a web-based environment. By using this book, professionals wishing to gain an understanding of the potentials of current access control techniques will be able to exploit existing solutions for specifying accurate protection requirements on their applications. The thorough analysis carried out in the book will also enable them to develop their own access control systems when necessary to deal with novel scenarios.