William Gropp has been named a fellow of the Association for Computing Machinery (ACM). The ACM Fellows Program recognizes outstanding members for their achievements in computer science and information technology and for their significant contributions to the mission of the ACM. Typically, only 20-30 fellows are named each year. Gropp joined Argonne National Laboratory in 1990 and is a senior computer scientist in the Mathematics and Computer Science Division. An outstanding example of Gropp's achievements was his initiation of the design and development of MPICH, an open-source implementation of the Message Passing Interface standard now widely used for solving scientific and engineering problems on parallel computers. MPICH2 won a prestigious R&D 100 award from R&D magazine in 2005. Complementing his research contributions is Gropp's leadership in high-performance computing. He was deputy scientific director of Argonne's Advanced Computing Research Facility, with responsibility for coordinating workshops, institutes, and classes in parallel computing and interacting with vendors and developers of new parallel computers. Subsequently he was executive director of Argonne 's Center for Computational Science and Technology, which has evolved and now features an IBM Blue Gene/L system. Gropp has coauthored more than 150 papers, is a senior fellow of the University of Chicago/Argonne Computation Institute, and has been series editor of the scientific computation section for MIT Press since 2003.