Ultra-faint dwarf galaxies are the smallest, most dark matter dominated, and least chemically enriched stellar systems in the universe, and are important targets for understanding dark matter and galaxy formation. They comprise by number the majority of galaxies in the universe, and not least, dwarf galaxies around the Milky Way provide crucial empirical input for verifying formation scenarios of our own galaxy. There are currently about sixty dwarf galaxies associated with the Milky Way and closer than about one million light-years; the Andromeda Galaxy, our closest large neighbor spiral galaxy, is two and one-half million light-years away.