Recent progress in understanding the structure of String theory has come from understanding the web of duality symmetries relating nonperturbative effects to perturbative ones. This proposal focuses on developing a better understanding of these various dualities and their implication to the nonperturbative theory underlying string theory. The PI will study the interrelationships among the web of gauged and ungauged supergravities in various dimensions. The PI will also investigate the phenomenological implications of string theory to gravitational physics, particle physics and cosmology. A related topic the PI will investigate is the noncommutative nature of space-time at very high energies.