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.