This book is intended as a study guide for the United States Medical Licensing Examination (USMLE) Step 1. The exam is the first step towards licensing for medical doctors in the United States. It is heavily weighted towards the basic sciences, including anatomy, physiology, biochemistry, and pathology. These topics are covered for each of the major organ systems, including the cardiovascular, respiratory, renal, gastrointestinal, and musculoskeletal systems. This book will cover each of these topics in the detail required for the USMLE Step 1.