OverviewThis monograph examines the interplay between behavioral and cognitive representations of attachmet during early childhood. We track the continued development of secure base support and use while assessing maternal co-construction processes and thier joint impact on children's secure base behavior and attachment representations. First, our investigation establishes that smoothly interacting dyads have mothers who continue to provide secure base support and children who use them as secure base across early childhood (mother sensitivity-child security links). Furthermore, the patterning of children's secure base behavior when interacting with the mother is related to the structure of children's knowledge about secure base relationships. Second, we introduce mother co-construction skills and evaluate their impact on the mother child relationship. Using two different co-construction tasks, we scored maternal co-construction in terms of skills that promote secure base script knowledge. Both tasks were related to maternal AAI coherence and attachment script knowledge. In addition, studies showed that maternal co-construction skills make unique contributions to both child secure base behvior and child script knowledge. Findings support the hypothesis that mothers' cognitive/verbal co-constructive skills during conversations about attachment and emotion-laden situations play a key role in organization of children's attachment behavior and representations. Finally, we demonstrate that maternal script knowledge not only impacts children's script knowledge (intergenerational transmission), but guides mothers' expectations and judgements of mother-child interactions. Throughout this monograph, we stress the importance of an interpersonal approach when investigating attachment relationships during early childhood, where mother-child interactions and communication about attachment-related issues are considered key to unveil co-constructive processes involved in the child's behavioral and cognitive organization of attachment relationships.