The use of mobile services is continuously growing and the technological and economic potential is not yet tapped. After the introduction of data bearer services in cellular communication systems, the mobile Internet access has been enabled. The Information Technology (IT) and the telecommunication (TC) domains began to merge and are still merging. In the IT domain the impact of XML Web Services has increased during recent years, since the Extensible Markup Language (XML) has been enforced as a meta language for structured information and its representation. This thesis presents concepts to integrate XML Web Services with mobile communication systems. The use of these technologies on terminals and network elements is discussed and extensions as well as enhancements are proposed. Amongst other topics, the so far passive role of the terminals is reconsidered. Terminals are going to be more intelligent and are going to provide services to each other as well as to network elements. Thereby, push and P2P services are going to be enabled without great development effort. Furthermore, protocol adjustments on the transport layer are proposed, which will significantly enhance the performance of Mobile Web Services. The concepts presented are implemented as prototypes and used in several practical applications in order to evaluate the benefits of these technologies for different MobileWeb Services use cases. The IP Multimedia Subsystem (IMS) is used as an integration platform for Web Services in the TC infrastructure. On one hand, the Mobile Web Service middleware forms an additional level of abstraction for application developers, on the other hand the middleware adjusts to the characteristic of the mobile communication system.