DESI is a multi-fiber optical spectrograph funded by the U.S. Department of Energy Office of Science. It will be conducted on the Mayall 4-meter telescope at Kitt Peak National Observatory. DESI will obtain optical spectra for tens of millions of galaxies and quasars, constructing a 3-dimensional map spanning the nearby universe to 10 billion light years. It will measure the effect of dark energy on the expansion of the universe, via various techniques such as the measurement of baryon acoustic oscillations. For more details, see: