MPICH is a high-performance and widely portable implementation of the Message-Passing Interface (MPI) standard. MPICH runs on parallel systems of all sizes, from multicore nodes to clusters to large supercomputers. Many of the largest systems on the Top500 list run MPICH. It also provides a vehicle for MPI implementation research and for developing new and better parallel programming environments. MPICH supports the latest version of the MPI standard, MPI-4. Current research in MPICH focuses on scalability to extreme-scale systems of the future.