This book provides a detailed overview on service architecture in the Telco, web and IT words. It proposes a general framework for better defining and describing communication service architectures. It aims both to formalize these architectures by using a syntax and a semantics that are common to different services, and on the other hand to respond to recurring questions about service design, such as the identification of the functional area of enablers or SOA (Service Oriented Architecture) services, the relevance of service compositions to the user or the collaboration between different services in a converging environment.