During the past 10 years nearly 80 studies on disorganized attachment involving more than 6,000 infant–parent dyads have been carried out. The current series of meta-analyses have established the reliability and discriminant validity of disorganized infant attachment. Although disorganized attachment behavior is necessarily difficult to observe and often subtle, many researchers have managed to become reliable coders. Furthermore, disorganized attachment shows modest short- and long-term stability, in particular in middle class environments, and it is not just a concomitant of constitutional, temperamental, or physical child problems. The predictive validity of disorganized attachment is established in terms of problematic stress management, the elevated risk of externalizing problem behavior, and even the tendency of disorganized infants to show dissociative behavior later in life. In normal, middle class families, about 15% of the infants develop disorganized attachment behavior. In other social contexts and in clinical groups this percentage may become twice or even three times higher (e.g., in the case of maltreatment). Although the importance of disorganized attachment for developmental psychopathology is evident, the search for the mechanisms leading to disorganization has just started. Frightening parental behavior may play an important role but it does not seem to be the only causal factor involved in the emergence of disorganized attachment.