In the early premature, the EEG is mostly discontinuous. Discontinuity becomes limited to quiet sleep periods by the 36th week of conceptional age (CA). Temporal theta bursts, or the "sawtooth" pattern, come and go between 27 and 32 weeks' CA. Delta brushes attain their maximum about 32 to 34 weeks' CA and disappear about 40 to 44 weeks' CA. Frontal sharp transients have their peak occurrence at 35 or 36 weeks' CA and are still present at 44 to 48 weeks' CA. The background activity is essentially symmetric but transient patterns are less symmetric and frequently asynchronous. Lack of variability in the record is abnormal after 34 weeks' CA. Responses to isolated light flashes are prominent from very early prematurity through full-term. On the other hand, photic driving is frequent in early prematures (29-32 weeks' CA), but it then declines and is difficult to detect in the full-term neonate. Nonspecific responses to stimulation occur from early prematurity. Sleep--waking cycles are clearly discernible about 37 weeks' CA. Active sleep (rapid eye movement) goes from 60% at 34 weeks' CA to the 25% of adulthood at about 8 months of age. The EEG of the full-term newborn has four patterns, corresponding to three states: the low voltage irregular for wakefulness, high voltage slow and tracé alternant for quiet sleep, and the mixed for either wakefulness or active sleep.