The Ensemble methodology supports the design and implementation of message passing applications, particularly MPMD and those demanding irregular or partially regular process topologies. In Ensemble applications are built by composition of modular message passing components. We outline the Ensemble Software Architecture (ESA) and give an overview of the concepts and its supporting tools. We present extensions of ensemble components for composing Grid applications and outline their transformation to pure MPI executables and their execution on MPICH-G2. We demonstrate by building two simple applications, one SPMD and one MPMD where the former SPMD code is reused.