  The recent years have brought great advances in our knowledge of magnetic
fields in cool giant and supergiant stars. For example, starspots have been
directly imaged on the surface of an active giant star using optical
interferometry, and magnetic fields have been detected in numerous slowly
rotating giants and even on supergiants. Here, I review what is currently known
of the magnetism in cool giant and supergiant stars, and discuss the origin of
these fields and what is theoretically known about them.
