  After a review of theoretical motivations to consider theories with direct
couplings of scalar fields to Ricci and gauge curvature terms, we consider the
dynamics and non-perturbative stabilization of a dilaton in three and in four
dimensions. In particular, we derive generalized Coulomb potentials in the
presence of a dilaton and discuss a low energy effective dilaton potential
induced by instanton effects and the S--dual coupling to axions. We conclude
with a discussion of cosmological implications of a light dilaton.
