Reviews selective behavioral, psychophysiological, and neuropsychological research bearing on how affective space should be parsed. Neither facial expression nor autonomic nervous system activity is found to provide unique markers for particular discrete emotions. The dimensions of approach and withdrawal are introduced as fundamental systems relevant to differentiating affective space. The role of frontal and anterior temporal asymmetries in mediating approach- and withdrawal-related emotion is considered. Individual differences in tonic anterior activation asymmetry are present and are relatively stable over time. Such differences are associated with an individual's propensity to display different types of emotion, mood, and psychopathology. The conceptual and methodological implications of this perspective are considered.