This article is concerned with thoracic outlet compression syndrome (TOCS), one of the most controversial subjects in medicine. It may also be the most underrated, overlooked, misdiagnosed, and probably the most important and difficult to manage peripheral nerve compression in the upper extremity. Contents of the chapter include the historical aspect, anatomy, etiology and incidence, pathophysiology, symptomatology, diagnosis, conservative and surgical treatment, other conditions associated with TOCS, and results of TOCS surgical treatment.