The lumbar and sacral plexuses are complex networks of spinal nerves that provide motor and sensory innervation to the lower trunk, pelvis, and lower limbs. The lumbar plexus, formed by the ventral rami of T12–L4 within the psoas major muscle, primarily innervates the anterior and medial compartments of the thigh. Unlike the brachial plexus, it lacks further trunks or cords but includes anterior and posterior divisions from L2 to L4. Main branches include the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves innervating muscles of the lower limb and extensive cutaneous regions.