  The Sloan Digital Sky Survey (SDSS) is the largest and most ambitious optical
CCD survey undertaken to date. It will ultimately map out one quarter of the
sky with precision photometry in five bands, high-quality astrometry, and
spectra of all galaxies and quasars brighter than certain limiting magnitudes.
The scientific potential of the SDSS is enormous and addresses a wide variety
of astrophysical key questions. After a proprietary period the reduced and
calibrated data are made available to the astronomical community as a whole.
  The SDSS is run by an international consortium involving universities and
research institutions. One of the participating partners is the Max Planck
Institute for Astronomy in Heidelberg. Already in its first year the SDSS has
led to a number of spectacular scientific discoveries. In this paper, we will
introduce the SDSS survey, discuss its scientific potential, highlight
important science results, and present the Calar Alto key program for SDSS
follow-up studies.
