Like many in the community of theoretical physicists, Professor Hawking is after the Grail of science-the Theory of Everything that lies at the heart of the cosmos. He involves us in the attempts at uncovering its secrets-from supergravity to supersymmetry, from quantum theory to M-theory, from holography to duality, and now, at the very frontiers of science, superstring theory and p-branes. He shares his eagerness to "combine Einstein's General Theory of Relativity and Richard Feynman's idea of multiple histories into a complete unified theory that will describe everything that happens in the universe." With characteristic exuberance, Hawking invites us to be fellow travelers on this extraordinary voyage through spacetime.