This volume is an excellent introduction to the principles and workings of optimality theory, a relatively new constraint-based framework. The focus is on phonology, which is where the theory thus far has had its greatest impact. A basic understanding of phonology and earlier rule-based derivational theories is assumed. At appropriate points, Kager distinguishes the different claims made by optimality theory and derivational theories. The exercises and suggested readings at the end of each chapter make the book highly suitable as a textbook. The conclusion of each chapter also provides a good summary of the main points. In addition to conventional subject and language indexes, a helpful index of constraints is included with page numbers for where the constraint is defined and used.