This review paper starts with some basic definitions of anatomical positioning nomenclature and isometry, examines the reasons for aiming for isometry and discusses the tensile properties of ligaments and grafts in the light of length changes imposed by knee motion. An examination of the biomechanics of different tibial and femoral graft attachments, and the effects of errors from isometric siting, leads into a review of previous literature of studies on the intact anterior cruciate ligament (ACL), ACL-deficient knees and then of ACL reconstructions. The discussion notes that there has been little work done to link the behaviour of reconstructed knees to that of the intact knees which the surgery is aiming to reproduce, and suggests that an anatomical graft placement, with the attachments eccentric to the isometric areas of intact knees, may approach this aim.