Abstract. In this paper we propose a constraint based declarative approach for Web services composition and monitoring problem. Our apllows user to build the abstract composition by identifying the participating entities and by providing a set of constraints that mark the boundary of the solution. Different types of constraints have been proposed to handle the composition modeling and monitoring. Abstract composition is then used for instantiating the concrete composition, which both finds and executes an instantiation respecting constraints, and also handles the process run-time monitoring. When compared to the traditional approaches, our approach is declarative and allows for the same set of constraints to be used for composition modeling and monitoring and ows for refining the abstract composition as a result of run-time violations, such as service failure or response time delays.