This paper describes Message Passing Interface 1 (MPI1), a proposed library interface standard for supporting point-to-point message passing. The intended standard will be provided with Fortran 77 and C interfaces, and will form the basis of a standard high level communication environment featuring collective communication and data distribution transformations. The standard proposed here provides blocking, nonblocking, and synchronized message passing between pairs of processes, with message selectivity by source process and message type. Provision is made for noncontiguous messages. Context control provides a convenient means of avoiding message selectivity conflicts between different phases of an application. The ability to form and manipulate process groups permits task parallelism to be exploited, and is a useful abstraction in controlling certain types of collective communication.