This article reviews the literature on embryology, anatomy, function, and biomechanics to define the properties of the native ACL. The discussion focuses on the ligamentous architecture and gross anatomy of the ACL including its femoral and tibial insertions as well as its midsubstance passing through the intercondylar fossa. Biomechanical modeling, mechanical and structural properties, and function of the ACL as a primary and secondary stabilizer under non-weightbearing and weightbearing conditions are described.