This rewrite of Message Passing Toolkit: MPI Programmer's Manual supports the 1.3 release of the Cray Message Passing Toolkit and the Message Passing Toolkit for IRIX (MPT). New features include MPI statistics, MPI I/O, thread-safe MPI, multiboard adapter selection, and other performance improvements. With the MPT 1.3 release, support for XMPI has been dropped.