Too many sleep specialists and technologists lament they lack sufficient training in recognizing abnormalities in the limited electroencephalography (EEG) channels recorded in a polysomnograph (PSG). Moreover, increasing numbers of patients with epilepsy, dementias, and extrapyramidal diseases are being referred to sleep centers, many of whom require recording of their PSGs with expanded EEG montages. This article reviews the range of normal, abnormal, and benign EEG variants encountered in patients undergoing PSG with conventional and expanded EEG montages. Because comprehensive in-laboratory PSGs are rarely requested for patients with severe acute encephalopathies, coma, or status epilepticus, discussion of these is omitted.