WFIRST will be an observatory, an experiment and a survey. With 100 times the field of view of Hubble and the same resolution, it will be able to be a powerful tool for conducting a survey of much of the infrared sky, complementing LSST’s optical observations. As a precision space-based telescope, WFIRST will use supernova, baryon acoustic oscillations to carry out a systematic study of the physics of cosmic acceleration. Through its microlensing survey of the galactic bulge, WFIRST will complete the demographic survey of extrasolar planets by detecting thousands of planets with separations greater than an astronomical unit and with mass down to below that of Mars. Its coronagraph should achieve contrast ratios a thousand times better than the Hubble telescope and the James Webb Space Telescope. This will greatly advance coronagraphy and produces images and spectra of giant planets around nearby stars.