Posterior shoulder instability only represents 2–10% of all patients with shoulder instability. With an incidence of 32.8 per 100,000 person-years, especially young active men between 14 and 19 years are affected. It’s etiology includes repeated microtrauma, single traumatic events, or atraumatic causes like general ligamentous laxity. In most cases dislocations of the shoulder are due to trauma, epileptic seizures, or electric shock injuries. Posterior instability is also reported as a secondary effect due to anatomical abnormalities including glenoid retroversion, large reverse Hill-Sachs injury, or glenoid dysplasia. To diagnose posterior shoulder instability, meticulous examination and radiographic imaging of the shoulder are necessary. This chapter discussed clinical examination and radiological imaging diagnostic tests for posterior shoulder instability, nonsurgical and surgical treatment interventions, and postsurgical rehabilitation.