The normal EEG doesn’t change much during adult life, but it must be interpreted in the context of physiological states (awake, drowsy, or asleep). Normal wakefulness is characterized by a reactive posterior dominant alpha rhythm, anterior faster beta activity, eye blink, and muscle artifact. Transition to drowsiness is typically characterized by attenuation of the posterior dominant rhythm, diffuse slowing into theta range, emergence of slow lateral eye movements, and dissipation of muscle artifact. Vertex waves are the architectural feature of stage I sleep. Positive Occipital Sharp Transients of Sleep (POSTS) may also occur. Sleep spindles and K complexes are the architectural feature of stage II sleep. Mitten waves are a normal variant, while dyshormia is abnormal. Slow wave sleep is characterized by diffuse high-amplitude semi-rhythmic delta slowing. Rapid eye movement sleep is characterized by eye movement artifact and sawtooth waves.