Relatively little has been written about one group of infants identified with Ainsworth's “Strange Situation” assessment of infant-parent attachment, those classified insecure/ambivalent. Although virtually all samples contain some insecure/ambivalent infants, these infants are uncommon, comprising 7%–15% of most American samples. Recently developed assessments of attachment in children and adults have identified attachment groups of older individuals thought to parallel the insecure/ambivalent infant group. Empirical work in which insecure/ambivalent individuals are examined as a separate group is reviewed within the context of attachment theory, and a coherent picture emerges of the antecedents (relatively low or inconsistent maternal availability; biological vulnerability) and sequelae (limited exploratory competence) of this group. This picture is used as the basis for additional theoretical proposals, and suggestions for future research are presented.