Background: Though noted in the clinical literature for more than 50 years, attachment disorders have been studied systematically only recently. In part because of the ubiquity of attachments in humans, determining when aberrant behavior is best explained as an attachment disorder as opposed to insecure attachment has led to some confusion. In this selective review, we consider the literature on reactive attachment disorder and disinhibited social engagement disorder and describe an emerging consensus about a number of issues, while also noting some areas of controversy and others where we lack clear answers. We include a brief history of the classification of the disorders, as well as measurement issues. We describe their clinical presentation, causes and vulnerability factors, and clinical correlates, including the relation of disorders to secure and insecure attachment classifications. We also review what little is known and what more we need to learn about interventions. Methods: We conducted a literature search using PubMed, PsycINFO, and Cochrane Library databases, using search terms "reactive attachment disorder," "attachment disorder," "indiscriminate behavior," "indiscriminate friendliness," "indiscriminate socially disinhibited reactive attachment disorder," "disinhibited social engagement disorder," and "disinhibited social behavior." We also contacted investigators who have published on these topics. Findings: A growing literature has assessed behaviors in children who have experienced various types of adverse caregiving environments reflecting signs of putative attachment disorders, though fewer studies have investigated categorically defined attachment disorders. The evidence for two separate disorders is considerable, with reactive attachment disorder indicating children who lack attachments despite the developmental capacity to form them, and disinhibited social engagement disorder indicating children who lack developmentally appropriate reticence with unfamiliar adults and who violate socially sanctioned boundaries. Conclusions: Although many questions remain to be answered, especially regarding appropriate interventions, we know considerably more about attachment disorders than we did only a decade ago.