Shoulder stiffness is defined as restricted passive and active range of motion (ROM) that can be primary (idiopathic) or secondary. The most consensual pathophysiology is that a primary insult to the shoulder triggers an inflammatory response with fibrosis and nerve tissue formation leading to shoulder stiffness and pain. It affects between 2% and 5% of the general population, most frequently women during the fifth to seventh decades of life. Predisposing factors include diabetes mellitus, thyroid and rheumatological diseases, hypoadrenalism, Parkinson disease, cardiopulmonary disease, cerebrovascular disease, Dupuytren contracture, trigger finger, and dyslipidemia. Primary stiff shoulder can resolve spontaneously with no treatment after 3–4 years. Most patients will have mild residual symptoms, and an average of 6% will have persistent severe residuals symptoms in the long term. Conservative therapy is the first-line treatment option in primary stiff shoulder. Surgery, with arthroscopic capsular release (ACR), is a viable alternative treatment option to provide earlier resolution of pain and restoration of shoulder function. In secondary stiff shoulder, the identification and treatment of the underlying cause of the restriction of ROM are essential. In either primary of secondary stiff shoulder, the timing of ACR is controversial. The purpose of the current chapter is to provide an overview of the current indications, technique, results, and complications of ACR for the treatment of stiff shoulder.