Harvard has had a long history of groundbreaking research in the theory of computation (ToC, also known as Theoretical Computer Science). This field addresses the mathematical laws that govern efficient computation, whether by human-made devices or natural phenomena. Today ToC had vastly expanded to touch many problems not just in computer science and engineering, but also pure and applied mathematics, as well as the natural, life and social sciences. Members of the ToC group at Harvard are pursuing both the fundamental questions of computation, as well as its applications to many areas, and are closely collaborating with colleagues across all of these fields.