The contribution of the event-related potential (ERP) research to understanding human selective attention will be evaluated. A closely related issue, the starting point of the present treatment, involves the nature and extent of automaticity in information processing. The mismatch-negativity component of the ERP suggests that the basic, obligatory, processing of the physical features of auditory stimuli is unaffected by the direction of attention. These data also reveal a possible mechanism for attention switching to stimulus change occurring in the unattended input, observed by cognitive psychologists. The N1 wave of the ERP might in turn provide a data base for explaining similar attention switches to stimulus onsets after breaks in stimulation and to offsets of long-duration stimuli. With regard to selective attention, the processing negativity might make it possible to delineate the central principle of stimulus selection in attention, a goal probably inaccessible to non-physiological attention research. In the visual modality, cognitive psychologists have found that spatial attention is more fundamental and powerful in stimulus selection than any other form of visual selective attention. Consistently, ERP data show that the exogenous components in vision are enhanced by spatial selective attention but not when attended and unattended stimuli are not spatially separated. Also, ERP data (the P3 wave) give support to certain forms of resource-allocation theories of attention. In addition, with regard to the currently popular distinction between automatic versus controlled processing, these data strongly suggest that extended consistent-mapping training does not lead to a "genuine" automatization of a search process in the sense of independence of a limited-capacity system.