Due to the ongoing controversy regarding the exact causes of injury in the thrower's shoulder, the authors will not attempt to provide a single unifying theory. Instead, we will provide an overview clarifying the terminology and describing common pathologic findings, and presenting the various theories on shoulder injuries in throwing athletes. The purpose of this chapter is to discuss the biomechanics, presentation, diagnosis and treatment of common shoulder injuries in overhead throwing athletes. For more studies on athletic shoulder injuries, please visit http://drmillett.com/shoulder-studies