  BPS saturated p-branes play an important role in recent progress in
understanding superstring theory and M theory. One approach to understanding
the dynamics of p-branes is to formulate an effective (p+1)-dimensional
world-volume theory. The construction of such brane actions involves a number
of interesting issues. One such issue is how to formulate the action for
theories that contain chiral bosons. The two main examples, which are the M
theory five-brane and the heterotic string, are described in this lecture.
Also, double dimensional reduction of the M theory five-brane on K3 is shown to
give the heterotic string.
