Rapid eye movement (REM) sleep behavior disorder (RBD), sleep paralysis, and nightmare disorder are the three REM sleep parasomnias outlined by the International Classification of Sleep Disorders. In this review we address the clinical neurophysiology of these disorders. The majority of neurophysiologic studies have been conducted in RBD, and fewer studies have evaluated patients with nightmare disorder or isolated sleep paralysis. Neurophysiologic studies of REM sleep parasomnias mostly used polysomnography (PSG), or were performed on animals to shed light on the pathophysiology of these disorders. Fewer studies used electoencephalography or electromyography outside the context of PSG, evoked potentials, or autonomic neurophysiologic studies. In this chapter, the main neurophysiologic findings in REM sleep parasomnias are described and their implications and relevance are discussed.