Quantitation has become an increasingly important part of clinical EMG. Most aspects of peripheral nerve and muscle function can be evaluated quantitatively using commonly available neurophysiologic methods. Because of the effects of collateral sprouting and reinnervation, techniques to measure the number of motor units supplying a muscle have been more difficult to develop. Motor unit number estimation (MUNE) consists of a number of different methods that evaluate the last unmeasured variable in nerve disease. The various MUNE techniques and their common technical issues will be reviewed, and potential clinical and research applications emphasized.