Pediatric rheumatology is a relatively new specialty, with many fascinating conditions peculiar to young people, virtually all of which are considered “orphan” diseases that are only rarely encountered by the generalist and therefore often present as diagnostic and therapeutic dilemmas. The popularity of the initial edition of this handbook suggested the need for a resource to fill the knowledge gap by assisting the pediatrician, the general practitioner, as well as rheumatologists with an interest in pediatric rheumatology, in the diagnosis and management of these diseases and problems. The emphasis has been placed on clinical presentation and how to arrive at a diagnosis, and an up-to-date management plan, using tables, algorithms, and figures as visual aids. Brief background information on the etiology is also provided. In this second edition we have added new knowledge accumulated since the first edition was published in 2007, particularly on new treatments for juvenile idiopathic arthritis and advances in the field of autoinflammatory diseases. We have also added a new chapter on tumors involving the musculoskeletal system. We sincerely hope that the information herein will help decrease the impact of these conditions on the children and their families by timely diagnosis and early intervention.