In the athlete, shoulder instability may result from external high-energy trauma or repetitive overuse. Our understanding of how shoulder instability may contribute to and result from shoulder injury has improved considerably during the past decade. In addition, the delicate balance between mobility and stability and the interrelationship between instability and rotator cuff disease make the clinical management of the unstable shoulder and its field treatment a challenge for physicians, therapists, trainers, and others responsible for the care of injured athletes.