Pervasivecomputingoffersenvironmentsinwhichuserneedsortasksarefulfilled without demanding their attention. This requires discovering a service or a set of services based on context (i.e. user presence, user activity, user location, temperature level,lightintensityleveletc.). Anatomicservicemaysometimesmeetthesimpleuser needs but meeting of complex user needs may lead to discovering a number of relevant services and composing them together. While the composed service may well serve userneeds,therecometimeswhenausermaywanttocustomizetheenvironmentbased on her preferences and this require adapting the composed service through parameter adjustment of one of its constituent services or a multiple constituent services. This makescontext-awarenessingeneralandcontextualservicecompositionandadaptation inparticularacorerequirementofpervasivecomputingapplications. Servicesavailable in the environment may be heterogeneous with regard to different discovery protocols (e.g., UPnP, SLP, JINI, etc.) being used fortheirpublication, discovery andinteraction. Context-aware service composition may involve discovery of heterogeneous services andtheadaptationofthecomposedservicemayinvolveinteractingwithheterogeneous constituent services. This raises the issue of service heterogeneity in context-aware service composition and adaptation. We have also proposed an approach following a separation of concerns, which allows adaptation decision logic (adaptation concern), a core part of context-aware applications, to be independently treated and managed as a separate unit of execution from the rest of application code. The proposed approach allows modelling of adaption concerns as declarative Event-Condition-Action (ECA) polices. This allows rapid development of context-aware applications and their dynamic modifiability. Another research issue that we address in this thesis is that of user involvement. Tothisend,wehaveproposedauser-centricapproachthatallowstheusertoparticipate in development of context-aware applications. To address aforementioned research challenges, we have designed and implemented a system whose detailed description is provided in the thesis. The system has been evaluated through usability,performance and scalability measures.