Message Passing Interface is a library specification. Programs written in sequential languages can take advantage of parallel computational resources by using this library. There are implementations for a wide variety of languages (including C, C++, and Java) and a variety of architectures (most flavors of Unix, Windows, and Mac OS 9).
This category contains instructional material about MPI, including manuals, tutorials, course notes, and other informative material. Note that many sites in the main MPI category will have their own documentation as well.