We present Ensemble, a message-passing implementation methodology, applied to PVM. Ensemble overcomes problems and complexities in developing applications in messagepassing environments (MPE). Applications are specified by scripts, which represent Process Communication Graphs (PCG) annotated with information specific for an MPE, and by reusable executable components. A loader program interprets the scripts and composes applications from reusable components. 1 Motivation The design and implementation of parallel message passing applications (MPA) have been recognized as demanding tasks. PVM [5] and MPI [6] Message Passing Environments (MPE) have improved the situation, as they permit the implementation of applications independently of the underlying architecture, but the step from application design to implementation remains, in general, a demanding task. The implementation does not only require the programming of sequential code solving a problem or providing a service, but also requi...