Bowlby’s attachment theory sheds new light on child development, particularly on interpersonal relationships. Experiments were conducted in order to categorize different patterns of attachment. A literature review confirms the bond between a secure pattern of attachment and the quality of friendly relationships. Nevertheless, one must distinguish the motivational system of attachment from the affiliative system directly involved in the establishment of friendly relationships. It seems that one of the systems is activated when the other is not. Studies trying to define the links and mediators between attachment and friendly relationships remain unconvincing.