The Wide-Field Infrared Survey Telescope (WFIRST) is a NASA observatory concept, now in phase A study, which is designed to perform wide-field imaging and slitless spectroscopic surveys for dark energy research and other astrophysical studies. It will also perform microlensing surveys to look for distant exoplanets in our galaxy, and direct imaging studies of some of the very nearest exoplanets. The current astrophysics focused telescope assets (AFTA) design of the mission makes use of an existing 2.4-m telescope, which yields enhanced sensitivity and imaging performance in all these science programs. AFTA also enables the addition of a coronagraph instrument (CGI) for direct imaging and spectroscopy of nearby giant exoplanets (including some that were discovered by radial velocity and other methods), and also for observing debris disks around the candidate host stars. This paper outlines the context for the other papers in this special volume on the WFIRST-AFTA CGI, covering the science, design, engineering, and technology development of the observatory and its CGI.