The study of attachment disorders has evolved over the last decades and a number of systematic studies have begun to illuminate the salient characteristics. Psychiatric nosologies have specified a variety of criteria for the disorder over the last 30 years, but there is emerging consensus regarding the disorders, their association with attachment, and ways in which to intervene with children affected by the disorder. In this chapter we review issues associated with defining attachment and attachment disorders, describe the typical development of attachment and examine the relationship between attachment classification, disorganized attachment, and attachment disorders. We discuss the history of attachment disorders including landmark studies by Tizard and colleagues, describe the progression of attachment disorders in the nosologies, and touch on the newest description to be found in the DSM-5. Finally, we examine measurement issues, review clinical course, and touch on interventions which address the amelioration of attachment disorders.