The programming of efficient parallel software typically requires extensive experimentation with program prototypes. To facilitate such experimentation, any programming system that supports rapid prototyping of parallel programs should provide high-level language primitives with which programs can be explicitly, statically, or dynamically tuned with respect to performance and reliability. Such language primitives should be able to refer conveniently to the information about the executing program and the parallel hardware required for tuning. Such information may include monitoring data about the current or previous program or even hints regarding appropriate tuning decisions. Language primitives and an associated programming system for program tuning are presented. The primitives and system have been implemented, and have been tested with several parallel applications on a network of Unix workstations.>