The National Center for Computational Sciences (NCCS) is a United States Department of Energy (DOE) Leadership Computing Facility that houses the Oak Ridge Leadership Computing Facility (OLCF), a DOE Office of Science User Facility charged with helping researchers solve challenging scientific problems of global interest with a combination of leading high-performance computing (HPC) resources and international expertise in scientific computing. The NCCS provides resources for calculation and simulation in fields including astrophysics, materials science, and climate research to users from government, academia, and industry who have many of the largest computing problems in science. The OLCF’s flagship supercomputer, the IBM AC922 Summit, is supported by advanced data management and analysis tools. The center hosted the Cray XK7 Titan system, one of the most powerful scientific tools of its time, from 2012 through its retirement in August 2019. The same year, construction began for Frontier, which is slated to debut as the OLCF’s first exascale system in 2021. (en)