A sample of 81 children was followed longitudinally to assess the contributions of behavioral inhibition, early attachment security, and experience of nonparental care to individual differences in social competence. Additive, mediational, and moderator models were tried. Attachment security was assessed in the Strange Situation at 15 months of age. Behavioral inhibition at 13?15 months and 4 years, and social competence at 8 years, were captured through aggregates of ratings and observations. Social competence was predicted by all three predictor variables, but for behavioral inhibition this was true only for the 4-year measure. The effects of attachment, nonparental care, and 4-year behavioral inhibition were found to be additive, supporting a view of social competence as multiply determined. There was also support for a moderating effect of attachment, meaning that a secure attachment relationship was particularly important for infants who started out as highly inhibited.