Functional popliteal artery entrapment is differentiated from anatomical entrapment by the absence of abnormal popliteal fossa anatomy. Although functional compression is a common entity in the general population, the precise etiology and natural history remains unknown. Magnetic resonance imaging clearly defines muscular variations within the popliteal fossa. In light of some of these variations, this article reviews embryological anatomy, diagnosis, classification, and treatment of the popliteal entrapment syndrome.