The original MPI standard was created by the Message Passing Interface Forum (MPIF). The public release of version 1.0 of MPI was made in June 1994. The MPIF began meeting again in March 1995. One of the first tasks undertaken was to make clarifications and corrections to the MPI standard. The changes from version 1.0 to version 1.1 of the MPI standard were limited to ``corrections'' that were deemed urgent and necessary. This work was completed in June 1995 and version 1.1 of the standard was released. This book reflects the updated version 1.1 of the MPI standard.