The anatomy and function of the median nerve is outlined in this chapter which includes many detailed illustrations. Motor and sensory branches of the median nerve are shown. Systematic details on how to test for median nerve extrinsic and intrinsic motor function are given with accompanying clear photographs. Testing for median nerve sensory function is also covered in this chapter. Lesions of the median nerve, including the three most common and well-known entrapment syndromes: carpal tunnel syndrome, pronator teres syndrome, and anterior interosseous syndrome, are discussed. The differentiation of high and low median nerve lesions is also included.