Abstract : Today there are many different scientific Grid workflow man- agement systems using a wide array of custom workflow languages. Some of them are geared towards a data-based view, some are geared towards a control-flow based view and others try to be as generic, and therefore often com- plex, as possible. All of these languages and custom work- flow management system front-ends fulfill special needs and workflow creation paradigms for their respective user com- munities. The problem is that once a workflow application has been created in one of these systems, it becomes very hard to share the workflow with users working with differ- ent systems. Portability and interoperability between cur- rent systems barely exists. In this work, we present a com- mon workflow language for use as an intermediate exchange representation by multiple workflow systems. It comprises atomic tasks, compound tasks including conditionals, se- quential and parallel loops as well as an expressive set of data types and data flow constructs.