  The INTEGRAL hard X-ray surveys have proven to be of fundamental importance.
INTEGRAL has mapped the Galactic plane with its large field of view and
excellent sensitivity. Such hard X-ray snapshots of the whole Milky Way on a
time scale of a year are beyond the capabilities of past and current narrow-FOV
grazing incidence X-ray telescopes. By expanding the INTEGRAL X-ray survey into
shorter timescales, a productive search for transient X-ray emitters was made
possible. In more than fifteen years of operation, the INTEGRAL observatory has
given us a sharper view of the hard X-ray sky, and provided the triggers for
many follow-up campaigns from radio frequencies to gamma-rays. In addition to
conducting a census of hard X-ray sources across the entire sky, INTEGRAL has
carried out, through Earth occultation maneuvers, unique observations of the
large-scale cosmic X-ray background, which will without question be included in
the annals of X-ray astronomy as one of the mission's most salient contribution
to our understanding of the hard X-ray sky.
