The Sloan Digital Sky Survey (SDSS) started a new phase in 2008 August,with new instrumentation and new surveys focused on Galactic structureand chemical evolution, measurements of the baryon oscillation featurein the clustering of galaxies and the quasar Lyα forest, and aradial velocity search for planets around ~8000 stars. This paperdescribes the first data release of SDSS-III (and the eighth countingfrom the beginning of the SDSS). The release includes five-band imagingof roughly 5200 deg2 in the southern Galactic cap, bringingthe total footprint of the SDSS imaging to 14,555 deg2, orover a third of the Celestial Sphere. All the imaging data have beenreprocessed with an improved sky-subtraction algorithm and a final,self-consistent photometric recalibration and flat-field determination.This release also includes all data from the second phase of the SloanExtension for Galactic Understanding and Exploration (SEGUE-2),consisting of spectroscopy of approximately 118,000 stars at both highand low Galactic latitudes. All the more than half a million stellarspectra obtained with the SDSS spectrograph have been reprocessedthrough an improved stellar parameter pipeline, which has betterdetermination of metallicity for high-metallicity stars.