Investigates how children’s security of attachment in infancy is related to various aspects of their cognitive development over the preschool years. The book thus constitutes an attempt to build bridges between the domains of social and cognitive development, and as such addresses issues which are of increasing interest to developmental psychologists. In the first two chapters it outlines Bowlby’s attachment theory and the research which it has inspired, and develops the theme of a secure attachment relationship providing children with a sense of themselves as effective agents in their interactions with the world (self-efficacy) The following chapters describe a study of a sample of children whose security of attatchment was assessed in infancy. Security-related differences are reported in the areas of object/person permanence, language aquisition. symbolic play, maternal tutoring and theory of mind, but no differances were found in general cognitive ability. The book’s major focus is explaining why securely attached children may be more self-effective and flexible in social interactions.