  The dwarf galaxy companions to the Milky Way are unique cosmological
laboratories. With luminosities as low as 10^-7 L_MW, they inhabit the lowest
mass dark matter halos known to host stars and are presently the most direct
tracers of the distribution, mass spectrum, and clustering scale of dark
matter. Their resolved stellar populations also facilitate detailed studies of
their history and mass content. To fully exploit this potential requires a
well-defined census of virtually invisible galaxies to the faintest possible
limits and to the largest possible distances. I review the past and present
impacts of survey astronomy on the census of Milky Way dwarf galaxy companions,
and discuss the future of finding ultra-faint dwarf galaxies around the Milky
Way and beyond in wide-field survey data.
