The iliopsoas refers to the joined psoas and the iliacus muscles. The two muscles are separate in the abdomen, but usually merge in the thigh. As such, they are usually given the common name iliopsoas. The iliopsoas muscle joins to the femur at the lesser trochanter. It acts as the strongest flexor of the hip.

The iliopsoas muscle is supplied by the lumbar spinal nerves L1-3 (psoas) and parts of the femoral nerve (iliacus).