Frozen shoulder is defined by loss of range of motion of the shoulder, impairing the patient’s ability to sleep, work, perform activities of daily living, or perform desired recreational activities. Etiology, pathology, natural history, diagnosis, and treatment have been debated. Cytokines, myofibroblasts, growth factors, and matrix metalloproteinases have all been implicated, and similarities to both Dupuytren contracture and Peyronie disease have been described. Frozen shoulder may be the end-stage manifestation of several primary conditions, including trauma, surgery, prolonged immobilization, endocrine disorders such as hypothyroidism or diabetes mellitus, and idiopathic causes. This condition generally affects patients 40 to 60 years of age and occurs in roughly 2% of the population but up to 18% of diabetic patients. The natural history of idiopathic frozen shoulder is variable but generally progresses in three stages, each 6 to 9 months in length: (1) inflammation (freezing), (2) fibrosis with disorganization and contracture (frozen), and (3) resolution (thawing). Although resolution generally occurs within 2 to 3 years in idiopathic frozen shoulder, some limitation of range of motion of questionable functional significance may be permanent. Because of the combination of inflammation and fibrosis seen on pathology, the terms frozen shoulder and adhesive capsulitis have been used interchangeably.