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environment, easy to program, to configure and to manage, based on standard software and protocols. The Grid is a large, distributed collection of Grid or Web services which offer computing, data storage, networking, and specialized simulations. Due to the dynamic nature of the Grid, workflow composition is a challenging task because the system has to deal with resource unreliability and unpredictability, which is closely related to fault tolerance and scheduling. In the framework of this Project we have developed and implemented (as a prototype) knowledge-based support for workflow construction and execution. The Grid system we have elaborated- semi-automatically composes a workflow of Grid services,- executes the composed workflow application,- monitors the performance of the Grid infrastructure and applications,- analyses the resulting monitoring information,- captures the knowledge contained in the information,- reuses the joined knowledge gathered from all participating users in a collaborative way in order to efficiently construct workflows for new Grid applications. In this way, the results of K-WfGrid close the gap between monitoring and workflow construction. K-WfGrid combines together and extends current achievements in Web Services, Semantic Web, Grid services and agent technologies to enable easier composition, execution and monitoring of workflows for real-life applications. The K-WfGrid system assists users in composing powerful Grid workflows by means of a rule-based expert system. The system adopts ontological descriptions of the environment and applications. We have developed a distributed knowledge base, a network of intelligent Grid services, as well as sophisticated performance monitoring and analysis, advanced user interfaces, and knowledge discovery