The tensor fasciae latae (TFL) is a small muscle on the lateral side of the hip. It originates from the iliac crest and inserts into the iliotibial band, which runs down the outer thigh to the tibia. It abducts, flexes, and internally rotates the hip, and stabilizes the pelvis and knee through tension on the iliotibial band. It is often tight in runners and can contribute to iliotibial band syndrome.