This paper has given an overview of the main features of MPI, but has not described the detailed syntax of the MPI routines, or discussed language binding issues. These are fully discussed in the MPI specification document. Since its first release in May 1994, MPI has rapidly become a popular message passing interface for parallel application programs and libraries. Several portable implementations of MPI exist, and major vendors are developing optimized versions for their own machines. The MPI Forum is currently considering extensions to MPI that will significantly expand its usefulness. The specification for these extensions is expected to be released in 1997. Further information about MPI, including the specification document and information about the portable implementations, may be obtained from the World-Wide Web. Two good starting points are http://www.epm.ornl.gov/~ walker/ and http://www.mcs.anl.gov/mpi.