This book examines Service Oriented Architectures (SOA) and Web Services, in particular focusing on the mobile domain. It presents a Contract First framework for platform-independent specification and automated implementation of Web Services adapters. For functionally and semantically interoperable implementation in the healthcare domain, HL7 is exemplarily addressed. The feasibility and appropriate­ness of the developed top-down approach is proven considering an implementation of a semi-mobile demonstrator HL7 Web Service. Finally, problems and future directions of Web Services, Mobile Web Services and Contract First development are analyzed.