This is the first book devoted solely to the subject of normal families of analytic and meromorphic functions since the 1927 treatise of Paul Montel. A considerable body of research has evolved since then, and this text provides a comprehensive treatment of the entire theory. Since its inception early this century, the notion of a normal family has played a central role in the development of complex function theory. In fact, it is a concept lying at the very heart of the subject, weaving a line of thought through Picard's theorems, Schottky's theorem, the Riemann mapping theorem, to many modern results on meromorphic functions via the Bloch principle. It is this latter which has provided considerable impetus over the years to the study of normal families, and continues to serve as a guiding hand to future work. Numerous applications of the normal family theory are discussed, particularly those found in the study of extremal problems, normal functions, harmonic functions, discontinuous groups, and complex dynamical systems. Only a basic knowledge of complex analysis and topology is assumed. All other necessary material for the study of the subject is included in the first chapter. The scope of the book ranges from advanced undergraduate to research level.