Shoulder instability is a common malady affecting the athlete's shoulder. A basic knowledge of shoulder anatomy and biomechanics is essential to understanding the pathophysiology and treatment options. The history and physical examination can lead the investigator to the correct diagnosis in most cases. Diagnostic imaging modalities can provide useful clues and help rule out concomitant pathology. Most patients are suitable candidates for a trial of shoulder rehabilitation. Those who fail nonoperative treatment may be candidates for surgical intervention. A variety of surgical techniques are available to reliably prevent recurrent instability. There has been a recent trend towards arthroscopic stabilization, including thermal capsulorrhaphy, which may prove as effective as open techniques.