The current study examined the relations between individual differences in sustained attention in infancy, the temperamental trait behavioral inhibition in childhood, and social behavior in adolescence. The authors assessed 9-month-old infants using an interrupted-stimulus attention paradigm. Behavioral inhibition was subsequently assessed in the laboratory at 14 months, 24 months, 4 years, and 7 years. At age 14 years, adolescents acted out social scenarios in the presence of an unfamiliar peer as observers rated levels of social discomfort. Relative to infants with high levels of sustained attention, infants with low levels of sustained attention showed increasing behavioral inhibition throughout early childhood. Sustained attention also moderated the relation between childhood behavioral inhibition and adolescent social discomfort, such that initial levels of inhibition at 14 months predicted later adolescent social difficulties only for participants with low levels of sustained attention in infancy. These findings suggest that early individual differences in attention shape how children respond to their social environments, potentially via attention's gate-keeping role in framing a child's environment for processing.