HI in galactic disks

Studies of the atomic phase of the interstellar medium, via the 21--cm spectral line of neutral hydrogen (H I), play a key rôle in our attempts to understand the structure and evolution of disk galaxies. We present here results from The H I Nearby Galaxy Survey (THINGS) and focus on the mass distribution as derived from the observed kinematics, and on the link between gas and star formation rate surface density, i.e., the Schmidt--Kennicutt law. Also, we briefly dwell on the wealth and wide variety of structures, often outlining what seem to be expanding shells surrounding sites of recent, massive star formation