The newest edition of Cassidy and Petty's Textbook of Pediatric Rheumatology is a comprehensive source of information regarding rheumatic diseases of childhood that is intended for physicians caring for these children. The authors wanted to include the important and extensive advances in understanding the pathogenic mechanisms of rheumatic diseases and the significant changes in their treatment. Thus, the fourth edition is not merely an update of earlier editions, but rather a complete revision. It is a thorough reference guide, encyclopedic in scope and detail. Particular attention has been paid to updating relevant references while also retaining classic and important historical ones.