Pervasive computing infrastructure makes it possible for mobile users to run software services on extremely heterogeneous and resource-constrained mobile devices. Heterogeneity and device limitedness creates serious problems for the development and deployment of mobile services that are able to run properly on the execution context and are able to ensures that users experience the “best” Quality of Service possible according to their needs and specific contexts of use. In this paper we show how the main issues related to the development of self-adapting context-aware services are addressed in the IST PLASTIC Project with the support of CHAMELEON, a declarative framework for tailoring adaptable services.