  It has been known that the fivebrane of type IIA theory can be used to give
an exact low energy description of N=2 supersymmetric gauge theories in four
dimensions. We follow the recent M theory description by Witten and show that
it can be used to study theories with N=1 supersymmetry. The N=2 supersymmetry
can be broken to N=1 by turning on a mass for the adjoint chiral superfield in
the N=2 vector multiplet. We construct the configuration of the fivebrane for
both finite and infinite values of the adjoint mass. The fivebrane describes
strong coupling dynamics of N=1 theory with SU(N_c) gauge group and N_f quarks.
For N_c > N_f, we show how the brane configuration encodes the information of
the Affleck-Dine-Seiberg superpotential. For N_c = and < N_f, we study the
deformation space of the brane configuration and compare it with the moduli
space of the N=1 theory. We find agreement with field theory results, including
the quantum deformation of the moduli space at N_c = N_f. We also prove the
type II s-rule in M theory and find new non-renormalization theorems for N=1
superpotentials.
