This book is a survey of the basic techniques for approximating combinatorial problems using parallel algorithms. Its core is a collection of techniques that can be used to provide parallel approximations for a wide range of problems, such as flows, coverings, matchings, traveling salesman problems, and graphs. For added clarity, the authors provide an introductory chapter containing the basic definitions and results. A final chapter deals with problems that cannot be approximated, and the book is rounded off by an appendix that gives a convenient summary of the problems described in the book. This book is an up-to-date reference for research workers in the area of algorithms and for graduate courses in the subject.