Three lectures on string field theory

There are several major theoretical developments whose goal is to achieve a fundamental understanding of the equations that govern the structure of string theory. In general, this basic structure is encoded in the interrelationship that exists between 2d conformal invariance and the spacetime gauge symmetries of the string theory. In an effort to formulate these explicitly, one has the approaches based on β-functions in 2d σ-models, S-matrix functionals, string field theory, integrable analytic geometry, loop space and others. In this lecture some of these approaches are reviewed and the interrelationships that exist among them are discussed. 79 refs