The SECAS Project (Simple Environment for Context Aware Systems) deals with the adaptation of applications to the context (user preferences and environment, terminal, etc.). We aim to develop a plat-form which makes the services, data and the user interface of applications adaptable to different context situations. In this domain, researches have concentrated on how to capture context data and how to carry it to the application. Our work focuses on the impact of context on the application core. In this ar-ticle, we present the architecture of SECAS, based on a definition of the context suitable for application adaptation, an adaptation strategy based on web services and a case study in the medical field.