While the Grid is becoming a common word in the context of distributed computing, users are still experiencing long phases of adaptability and increased complexity when using the system. Although users have access to multiple resources, selecting the optimal resource for their application and appropriately launching the job is a tedious process that not only proves difficult for the naïve user, but also leads to ineffective usage of the resources. A general-purpose resource broker that performs application specific resource selection on behalf of the user through a web interface is required. This paper describes the design and prototyping of such a resource broker that not only selects a matching resource based on user specified criteria but also uses the application performance characteristics on the resources enabling the user to execute applications transparently and efficiently thereby providing true virtualization. © Springer-Verlag Berlin Heidelberg 2005.