  This paper describes the fourth data release of the Sloan Digital Sky Survey
(SDSS), including all survey-quality data taken through June 2004. The data
release includes five-band photometric data for 180 million objects selected
over 6670 deg^2, and 673,280 spectra of galaxies, quasars, and stars selected
from 4783 deg^2 of that imaging data using the standard SDSS target selection
algorithms. These numbers represent a roughly 25% increment over those of the
Third Data Release. The Fourth Data Release also includes an additional 131,840
spectra of objects selected using a variety of alternative algorithms, to
address scientific issues ranging from the kinematics of stars in the Milky Way
thick disk to populations of faint galaxies and quasars.
