  We argue that all conjectured dualities involving various string, M- and F-
theory compactifications can be `derived' from the conjectured duality between
type I and SO(32) heterotic string theory, T-dualities, and the definition of
M- and F- theories. (Based on a talk given at the conference on `Advanced
Quantum Field Theory', Le Londe-les-Maures, France, Aug.31-Sept.5, 1996, in
memory of Claude Itzykson)
