  I review the effects of magnetic fields on star formation in galaxies. This
includes the effects of the magnetorotational instability (MRI) at galactic
scales, magneto-Jeans and swing instabilities, Parker instabilities, and the
effects of magnetic fields on the evolution of supernova-driven turbulence. I
argue that currently turbulent support by the MRI appears likely to be the most
important of these processes to regulating star formation.
