Traditional non invasive electromyography (EMG) is based of differential amplification of a signal detected with two electrodes: either one on the muscle of interest and one at a `reference potential` (monopolar) or both on the muscle of interest (bipolar or single differential). The location of these electrodes is critical and the information provided is limited. Linear or two-dimensional arrays placed on the muscle of interest imply multichannel recording, amplification and processing, but provide a great amount of information, from which the location of the innervation zones can be detected, as well as the features of individual motor units. This information is useful in a variety of applications, ranging from neurophysiology (monitoring control strategies and fatigue of individual motor units), to rehabilitation (assessing effectiveness of treatment), to ergonomics (designing proper workstations), to gynecology (preventing incontinence caused by episiotomy). Basic concepts and applications will be presented.