Myoclonus can be diagnosed and classified mainly based on clinical features. Neurophysiologic studies help confirm clinical diagnosis and classification, and understand underlying physiological mechanisms. The neurophysiologic classification of myoclonus is mainly based on surface EMG (individual EMG patterns, muscle spatial distribution and time sequence of muscle activation), EEG, EEG/EMG relationships (jerk-locked back-averaging, cortico-muscular coherence), somatosensory evoked potentials, and long-loop reflexes. Paired stimulation evoked response/long loop reflex and jerk-locked evoked responses evaluate the excitability changes of the primary somatosensory cortex. Transcranial magnetic stimulation can evaluate the excitability state of the primary motor cortex.