This book constitues the refereed proceedings of the 4th International Symposium on Abstraction, Reformulation, and Approximation, SARA 2000, held at Lake LBJ, Texas, USA in July 2000. The nine revised full papers presented together with five extended abstracts, three posters, seven research summaries, and four invited papers were carefully reviewed and selected for inclusion in the book. The book addresses all current aspects of abstraction, reformulation, and approximation and applications in areas like automatic programming, constraint satisfaction, design, diagnosis, inductive logic programming, computational learning, planning, resource allocation, theorem proving, qualitative reasoning, relational databases, etc.