The Nancy Grace Roman Space Telescope, formerly WFIRST, was the top-ranked large space mission in the Astro2010 Decadal Survey. It will obtain a wide-field survey of the sky and observe exoplanets. The survey will cover a region of more than 2,000 square degrees at near-infrared (0.6-2 microns) wavelengths. The Roman Space Telescope will employ three independent techniques to determine the effect of dark energy on the evolution of the universe. The mission will also collect statistics on exoplanets around a large sample of stars and will directly detect exoplanets with a coronograph. In addition, the Roman Space Telescope will survey our galaxy and others nearby to answer key questions about their formation and structure and provide constraints on how galaxies grow. The mission will take approximately 10 years to develop.