  I review detached binaries consisting of white dwarfs with either other white
dwarfs or low mass main-sequence stars in tight orbits around them. Orbital
periods have been measured for 15 white dwarf/white dwarf systems and 22 white
dwarf/M dwarf systems. While small compared to the number of periods known for
CVs (>300), I argue that each variety of detached system has a space density an
order of magnitude higher that of CVs. While theory matches the observed
distribution of orbital periods of the white dwarf/white dwarf binaries, it
predicts white dwarfs of much lower mass than observed. Amongst both types of
binary are clear examples of helium core white dwarfs, as opposed to the usual
CO composition; similar systems must exist amongst the CVs. White dwarf/M dwarf
binaries suffer from selection effects which diminish the numbers seen at long
and short periods. They are useful for the study of irradiation; I discuss
evidence to suggest that Balmer emission is broadened by optical depth effects
to an extent which limits its usefulness for imaging the secondary stars in
CVs.
