This study investigated the relation between maternal contingent responsiveness and 4- and 5-month-old infants' (N = 64) social expectation behavior in a still-face procedure. Mothers were asked to interact with their infants for 2 min (interactive phase), remain still-faced for 1 min (still-face phase), and resume interaction for 2 min. Mother and infant behavior was assessed for the frequency of infant and mother smiles, mother smiles that were contingent to infant smiles and infant smiles were contingent to mother smiles during the interactive phase, and infant social bids to mother during the still-face phase. Hierarchical regression showed that mother contingent smiles during the interactive phase accounted for unique variance in infant social bids during the still-face phase beyond that accounted for by the frequency of mother and infant smiles during the interactive phase. These results support the view that young infants' social expectations and sense of self-efficacy are formed within their interactions with their caregivers. (Contains 4 tables and 2 footnotes.)