Leslie G. Valiant, the T. Jefferson Coolidge Professor of Computer Science and Applied Mathematics at Harvard University, has made far-reaching contributions to the study of computational complexity, parallel computation, and learning theory. Educated at King’s College, Cambridge, where he studied mathematics, he went on to earn a DIC in computer science at Imperial College, London, and was awarded a Ph.D. in computer science by Warwick University in 1974. He taught at Carnegie Mellon University, Leeds University, and the University of Edinburgh before joining the Harvard computer science faculty as Gordon McKay Professor of Computer Science and Applied Mathematics in 1982. Dr. Valiant was named to his present chair in 2001. His work in theoretical computer science includes developing a formal system, called robust logics, that is intended to reconcile the apparent logical nature of reasoning and the statistical nature of learning, as well as finding computational explanations of how the brain performs its basic tasks of learning and memory. Very recently he has proposed a theory of evolvability that views evolution as a restricted form of learning. Dr. Valiant is a fellow of The Royal Society and a member of the National Academy of Sciences. Recipient of the Nevanlinna Prize in 1986 and the Knuth Prize in 1997, he has published some eighty-five papers in scientific journals. He is also the author of the widely-acclaimed Circuits of the Mind (Oxford University Press, 1994 and 2000) in which he details a promising new computational approach to studying the workings of the human brain.