  We review the properties of 40 X-ray binaries that contain either a confirmed
black hole or a black hole candidate. After discussing briefly the significance
of these Galactic black holes to both astronomy and physics, we present basic
data for all 40 systems, review the physics of mass accretion onto black holes,
and then show seven-year light curves of 20 systems. The second half of this
work is a far-reaching review of the canonical emission states of black hole
binaries, which is based on X-ray, radio and gamma-ray data. For several
selected black holes, we show 33 pairs of X-ray energy and power density
spectra and use these spectra as a basis for introducing modified definitions
of the canonical X-ray emission states of an accreting black hole. We highlight
the physical structures and some of the emission mechanisms associated with
each emission state. In the final pages we examine both low- and high-frequency
quasi-periodic oscillations. A recurring theme of the review is the importance
of these black holes as potential sites for tests of general relativity.
Accordingly, we stress phenomena that originate in strong gravity, such as
relativistic Fe emission lines and thermal continuum emission, both of which
arise in the inner accretion disk. Especially important in this regard are the
high-frequency (40-450 Hz) quasi-periodic oscillations observed for seven black
holes, three of which show evidence for commensurate (3:2) pairs of
frequencies.
