Remarks on the M5-Brane

The fivebrane of M theory -- the M5-brane -- is an especially interesting object. It plays a central role in a geometric understanding of the Seiberg-Witten solution of N=2 D=4 gauge theories as well as in certain new 6d quantum theories. The low energy effective action is an interacting theory of a (2,0) tensor multiplet. The fact that this multiplet contains a two-form gauge field with a self-dual field strength poses special challenges. Recent progress in addressing those challenges is reviewed.