In light of evidence that the effects of attachment security on subsequent development may be contingent on the social context in which the child continues to develop, we examined the effect of attachment security at age 15 months, cumulative contextual risk from 1 to 36 months, and the interaction of attachment and cumulative risk to predict socioemotional and cognitive linguistic functioning at age 3 years, using data from the National Institute of Child Health and Human Development Study of Early Child Care. Results indicated that early attachment predicts both socioemotional development and language skills, but not cognitive functioning as indexed by a measure of school readiness, and that the effect of attachment on socioemotional development and expressive language varied as a function of social-contextual risk. Insecure–avoidant infants proved most vulnerable to contextual risk, not children classified as secure or insecure more generally, although in one instance security did prove protective with respect to the adverse effects of cumulative contextual risk. Findings are discussed in terms of risk and resilience and in light of the probabilistic nature of the relation between early attachment and later development.