In this longitudinal study, the authors tested a developmental hypothesis derived from attachment theory and recent empirical findings. Target participants were 78 individuals who have been studied intensively from infancy into their mid-20s. When targets were 20–23 years old, the authors tested the way in which interpersonal experiences at 3 pivotal points in each target's earlier social development—infancy/early childhood, early elementary school, and adolescence—predicted the pattern of positive versus negative emotions experienced with his or her romantic partner. A double-mediation model revealed that targets classified as securely attached at 12 months old were rated as more socially competent during early elementary school by their teachers. Targets' social competence, in turn, forecasted their having more secure relationships with close friends at age 16, which in turn predicted more positive daily emotional experiences in their adult romantic relationships (both self- and partner-reported) and less negative affect in conflict resolution and collaborative tasks with their romantic partners (rated by observers). These results are discussed in terms of attachment theory and how antecedent life experiences may indirectly shape events in current relationships.