The iliotibial tract, otherwise known as the iliotibial band, or the band of Maissiat, is a ligament connecting the ilium with the tibia. It is observed in its form in man and is associated with the erect posture. It is connected intimately with the tensor fasciae latae anteriorly and the glutaeus maximus posteriorly in the region below the greater trochanter. As a result of this study, the author feels that the femur is stabilized synergistically by the tensor fasciae latae and glutaeus maximus in standing and walking. The tensor fasciae latae pulls the tense band anteriorly in flexion; the glutaeus maximus shifts the band posteriorly in forced extension. The band is, however, held by the lateral intermuscular septum permitting a limited amount of anteroposterior motion. At the knee joint, the band acts as a stabilizing ligament between the lateral femoral condyle and the tibia in continuity with the proximal part of the band. This stabilizing ligament is attached to the upper portion of the lateral femoral condyle as a fixed point, and moves with the lateral tubercle of the tibia (the tubercle of Gerdy) forward in extension and backward in flexion of the knee joint. The importance of the tensor fasciae latae and of the iliotibial tract has been, possibly, overestimated as a deforming factor in patients with paralyses and contractures.