Needle electromyography (EMG), i.e., extracellular recording of action potentials of muscle fibers with intramuscular electrodes, is a valuable diagnostic method in clinical medicine. It allows the recognition of different types of spontaneous activity, e.g., fibrillation potentials due to denervation, as well as changes in the motor unit potentials related to various disease processes, such as primary muscle diseases, disorders of the neuromuscular junction, or injuries to the peripheral nerves. The technical refinements and the introduction of automated methods of signal analysis made possible by the advent of new technologies have greatly increased versatility of needle EMG, as well as its diagnostic sensitivity and specificity. Physical properties of the EMG signals, characteristics of recording electrodes, features of the recording equipment and the stored data format are among important technical aspects of the method.