Description:This book provides a comprehensive categorical theory of closure operators, with applications to topological and uniform spaces, groups, R-modules, fields and topological groups, as well as partially ordered sets and graphs. In particular, closure operators are used to give solutions to the epimorphism and co-well-poweredness problem in many concrete categories. The material is illustrated with many examples and exercises, and open problems are formulated which should stimulate further research. Audience: This volume will be of interest to graduate students and professional researchers in many branches of mathematics and theoretical computer science. Knowledge of algebra, topology, and the basic notions of category theory is assumed.