We will report on recent advances in the understanding of non-perturbative
interconnections between different string dualities. Weak-strong coupling
duality (S-duality) and T-duality (symmetry under compactification on dual
tori) allows one to compare and explore the strong coupling regime of seemingly
unrelated theories. These theories naturally merge in a quantum version of
supergravity called M-theory. The dynamical role of `branes' of different
nature and the new dynamical tool of (M)atrix formulation of M-theory will be
briefly mentioned.Comment: 12 pages, LaTeX; Plenary Talk given at the XII International Congress
of Mathematical Physics, 13-19 July 1997, Brisbane, Australi
