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.