  The black hole at the center of our Milky Way Galaxy -- the Galactic Black
Hole, or GBH -- is a rather modest representative of its class. With a mass of
4 x 10^6 solar masses, it is well over a thousand times less massive than the
most extreme supermassive black holes known to be powering the most luminous
quasars. Furthermore, the Galactic Black Hole has a remarkably dim accretion
flow, and its luminous energy output is overwhelmed by the dense cluster of
bright stars and red giants that surround it, except at radio wavelengths.
However, the proximity of the GBH compensates for its restrained activity;
being over 100 times closer than the next nearest supermassive black hole in a
galactic nucleus, it offers us an unparalleled opportunity to observe its
behavior in detail. Consequently, far more observational attention has been
paid to the GBH and its entourage of stars and gas than to any other single
object outside the solar system. This review covers the history of our
recognition of the GBH, its presently known physical characteristics, the
manifestations of its current and past activity, and the prospects for refining
our knowledge with future research.
