Despite significant progress in the development of Grid infrastructure, the provisioning of a customized and controllable remote execution environment remains an open issue. This paper introduces the concept of a virtual workspace, a configurable execution environment that can be created and managed as a first-class entity to reflect client requirements. Such workspaces can be dynamically deployed on a variety of resources decoupling the notion of environment and resource. We show how virtual workspaces fit into the Grid architecture, present an example implementation using virtual machines, and discuss our initial experiences using this system in practice and with applications.