Definition as well as classification of myoclonus and electrophysiologic methods for investigating myoclonus were reviewed. Among the electrophysiologic techniques currently available in most laboratories, the EEG-EMG polygraph is the most essential one and can provide us with the most important information. Jerk-locked averaging and evoked potential studies are useful for further investigating the pathophysiology of myoclonus and can be performed by using the same recording electrodes as those used for the polygraph. Jerk-locked evoked potentials and double-stimulation evoked potentials can be employed only for further investigating how cerebral cortex is involved in the generation of certain myoclonia. All these techniques can be used in proper combinations depending on the clinical features of the myoclonus in question, the purpose of the study, and the facilities available in each laboratory. These techniques also will be useful for following the clinical course during the treatment with antimyoclonus agents.