  I discuss some of what is known and unknown about the behavior of black hole
binary systems in the quiescent accretion state. Quiescence is important for
several reasons: 1) the dominance of the companion star in the optical and IR
wavelengths allows the binary parameters to be robustly determined - as an
example, we argue that the longer proposed distance to the X-ray source GRO
J1655-40 is correct; 2) quiescence represents the limiting case of an extremely
low accretion rate, in which both accretion and jets can be observed; 3)
understanding the evolution and duration of the quiescent state is a key factor
in determining the overall demographics of X-rary binaries, which has taken on
a new importance in the era of gravitational wave astronomy.
