The anatomy, motor function, and sensory function of the ulnar nerve are outlined in this chapter with multiple explanatory illustrations and photographs. Methods of testing for ulnar nerve motor and sensory function are clearly explained including adduction of the fingers, abduction of the fingers, and adduction of the thumb. Lesions of the ulnar nerve—cubital tunnel syndrome and ulnar tunnel syndrome (Guyon’s canal)—and ulnar claw hand are also described.