The development of the attachment behavioral system in infancy has been the focus of a wide range of research in the past 30 years. The clinical significance of disturbances in this area of development is currently a major focus for this research. Research on patterns of attachment in infancy has informed understanding of the development of psychopathology in later childhood; insecure-disorganized attachment is recognized as an important risk factor in this regard. The clinical features of reactive attachment disorder in early childhood are also becoming more clear. Finally, knowledge about the intersection between attachment and various risk conditions is growing and should inform clinical judgement about infants and young children requiring intervention. Primary care physicians can use these findings to identify children in need of intervention.