This book constitutes the refereed proceedings of the Third International Symposium on Theoretical Aspects of Computer Software, TACS'97, held in Sendai, Japan, in September 1997. The book presents 20 revised full papers selected from a total of 46 submissions. Also included are seven invited papers by internationally leading scientists. Among the topics addressed are action calculi, polymorphisms, type theory, lambda calculi, refinement, finite transition systems, model checking, process algebras, logical frameworks, higher-order logics, etc.