MPI-3.1 is a minor update to the MPI standard. Most of the updates are corrections and clarifications to the standard, especially for the Fortran bindings. New functions added include routines to manipulate MPI_Aint values in a portable manner, nonblocking collective I/O routines, and routines to get the index value by name for MPI_T performance and control variables. A general index was also added. Any valid MPI-3.0 program is a valid MPI-3.1 program.