MPI (the Message Passinag Interface) is a widely used standard for distributed-memory programming on HPC (High Performance Computing) systems. MPI allows exchanging data (_messages_) between programs running in parallel. There are several high-quality open source MPI implementations (e.g. MPICH, MVAPICH, OpenMPI) as well as a variety of closed-source implementations. These libraries can typically make use of high-bandwidth low-latency communication hardware such as InfiniBand. This library mpi-hs provides Haskell bindings for MPI. It is based on ideas taken from haskell-mpi, Boost.MPI for C++, and MPI for Python. mpi-hs provides two API levels: A low-level API gives rather direct access to the actual MPI API, apart from certain "reasonable" mappings from C to Haskell (e.g. output arguments that are in C stored via a pointer are in Haskell regular return values). A high-level API simplifies exchanging arbitrary values that can be serialized. Note that the automated builds on Hackage will currently always fail since no system MPI library is present there. However, builds on Stackage should succeed -- if not, there is an error in this package.