Mother-infant face-to-face interaction is central to infant socioemotional development. Little has been known about the mechanisms that mediate the mother's influence. Findings are reviewed from a series of laboratory studies that suggest the major functional components of a mother's behavior are its affective quality and its contingent relationship to her baby's behavior. Quality of mother's affective expression accounted for individual differences in the behavior of thirteen 7-month-old infants living in multiproblem families. Infants' response was specific to the type of affective expression mothers displayed. Flat, withdrawn maternal affective expression was associated with infant distress. Intrusive maternal expression was associated with increased gaze aversion. Lack of contingent responsiveness was common to all but four mothers. Findings suggest that withdrawn or intrusive maternal affective expression, together with lack of contingent responsiveness, may in part be responsible for the risk-status of infants in multiproblem families.