  We summarize the HI properties of early-type galaxies, in particular the
differences in HI morphologies observed in early-type galaxies of different
luminosities. We find that in low-luminosity early-type galaxies the HI is
almost always in a disk-like structure, with central surface densities high
enough for star formation to occur. In a few luminous early-type galaxies the
HI is also in a disk or in a ring-like structure, but in most luminous
early-type galaxies the HI has a relatively irregular morphology. The surface
densities in the HI disks in luminous early-type galaxies are lower than in the
HI disks in low-luminosity early-type galaxies and no large-scale star
formation should occur in these disks. We discuss these different HI
characteristics in the context of other properties of early-type galaxies that
correlate with luminosity.
