Theory and research on adult attachment style emphasize the crucial role that the sense of attachment security plays in the formation and maintenance of couple relationships. In the present article, we review studies that have examined the contribution of adult attachment style to relational cognitions, emotions, and behaviors as well as to the formation, quality, and stability of dating and marital relationships. We discuss some of the measurement and design issues raised by this research. Based on the reviewed findings, we provide an integrative, systemic theoretical model delineating how the links between partners' attachment security and the quality of their couple relationship occurs. Finally, we discuss the implications of this model for the understanding of how attachment style and couple relationships combine to affect the family system in general, and parent-child relationships and children's developmental outcomes, in particular.