  This is the text of a talk given at the Inaugural Conference of the Asia
Pacific Center for Theoretical Physics, Seoul, Korea, June 9, 1996. If nature
is described by string theory, and if the compactification radius is large (as
suggested by the unification of couplings), then the theory is in a regime best
described by the low energy limit of $M$-theory. We discuss some
phenomenological aspects of this view. The scale at which conventional quantum
field theory breaks down is of order the unification scale and consequently
(approximate) discrete symmetries are essential to prevent proton decay. There
are one or more light axions, one of which solves the strong CP problem.
Modular cosmology is still problematic but much more complex than in
perturbative string vacua.
