Abstract
Normally we think of galaxies as gravitationally bound associations of
stars. Other baryonic components, like gas and dust, are minority
constituents. However, some dwarf galaxies are dominated by atomic gas,
in the sense that this component outweighs the stars. These objects
provide unique tests of galaxy formation theory, probe an environment
where star formation is remarkable inefficient, and may provide the key to
calibrating the Baryonic Tully-Fisher relation.