  In this semi-technical review we discuss string theory (and all that goes by
that name) as a framework for a quantum theory of gravity. This is a new
paradigm in theoretical physics that goes beyond relativistic quantum field
theory. We provide concrete evidence for this proposal. It leads to the
resolution of the ultra-violet catastrophe of Einstein's theory of general
relativity and an explanation of the Bekenstein-Hawking entropy (of a class of
black holes) in terms of Boltzmann's formula for entropy in statistical
mechanics. We discuss `the holographic principle' and its precise and
consequential formulation in the AdS/CFT correspondence of Maldacena. One
consequence of this correspondence is the ability to do strong coupling
calculations in SU(N) gauge theories in terms of semi-classical gravity. In
particular, we indicate a connection between dissipative fluid dynamics and the
dynamics of black hole horizons. We end with a discussion of elementary
particle physics and cosmology in the framework of string theory. We do not
cover all aspects of string theory and its applications to diverse areas of
physics and mathematics, but follow a few paths in a vast landscape of ideas.
(This article has been prepared for the TWAS Silver Jubilee)
