This grant funds a fourth phase of the Sloan Digital Sky Survey (SDSS IV), a pioneering astronomical survey that utilizes a 2.5 meter optical telescope at Apache Point Observatory near Cloudcroft, New Mexico. Over the next six years, SDSS IV will pursue three innovative projects that seek to answer key questions in astronomy and astrophysics. The first project, APOGEE-2, will decipher the history of the growth of the Milky Way's stellar halo; precisely measure the mass of the Milky Way; determine the stellar structure around the galactic center; find stellar companions such as planets, white dwarfs and neutrons stars; and determine stellar masses, ages, and elemental abundances with unprecedented precision. The second, MaNGA will study 6,700 nearby galaxies and measure their dynamics, growth histories, and chemical abundances as a function of their mass, type, environment, and other controlling variables. The third, eBOSS, will measure the expansion of the universe over the past 12 billion years using baryonic acoustic oscillation, the most accurate absolute distance measurement technique known, and filling a gap in current measurements of galaxies between about 6.5 and 11 billion light?years away. eBoss will provide the fullest understanding yet of the so-called "dark energy" that is causing the expansion of the universe to accelerate. As in previous phases of the projects, all SDSS data will be publically released through the internet, enabling astronomers and astrophysicists all over the world to use the data for their own research.