Driven by the emergence of mobile and ubiquitous computing there is a growing demand for context-aware applications that can dynamically adapt to their runtime environment. Middleware support for providing such adaptation to mobile applications has been an attractive research and development issue for several years now. However, one of the major challenges to support adaptation is that they can not be always foreseen during the design time. In a ubiquitous computing environment, a number of mobile devices running adaptive applications supported by the instances of the same middleware may come and go in a particular adaptation domain in an unanticipated manner. Moreover, third party services may also appear and disappear with respect to that particular adaptation domain. In componentbased application architectures, with the enhancement of integrating services, mobile applications may benefit from using the components that are provided by other users as well as using third party services. At runtime the application is composed of the components and the services available within the adaptation domain. This thesis provides an approach, including theoretical background, an adaptation middleware, an MDA-based application development methodology and a tool chain, in order to solve such unanticipated adaptation problems.