2 studies were undertaken to assess the positive affective correlates of secure attachment in infancy and to assess the relation between secure attachment in infancy and competence in the peer group at age 3 1/2 years. In study 1, smiling and smiling combined with vocalizing and/or showing toys distinguished securely from anxiously attached infants during free play at age 18 months. Rated quality of affective sharing distinguished securely from anxiously attached infants during free play at 18 months and 24 months. Thus, secure attachment involves more than the absence of negative or maladaptive behavior directed toward a caregiver. Study 2 assessed cross-age, cross-situational, and cross-behavioral consistency in quality of social adaptation. Quality of infant-mother attachment relationships at age 15 months was related to Q-sort assessments of personal and interpersonal competence in the preschool play-group at age 3 1/2 years. The results contribute to the validation of attachment as an important developmental construct. They also suggest that age appropriate assessment of developmental social competence constructs can be a useful alternative to the study of homotypic behavioral continuity.