Myoclonus is defined as sudden, brief, shock-like involuntary movements affecting one or more muscles. The term encompasses a wide range of different physiologic and pathologic processes. When evaluating a patient with myoclonus, the first step is to identify the underlying etiology. Initial treatment should be directed against any underlying toxic or metabolic conditions. Next, targeted pharmacotherapy should be chosen, principally on the basis of the probable anatomical localization. Although treatment is initiated with a single agent, polytherapy usually is necessary to achieve adequate symptomatic control. The prognosis of myoclonus is highly variable, and largely depends on the underlying cause.