All children who enter foster care have experienced disruptions in their relationships with caregivers, and many have experienced maltreatment. Studying the effects of these adverse early experiences can inform developmental theory. In particular, insight can be provided regarding sensitive periods in the development of attachment and self-regulatory capabilities. The quality of surrogate caregivers varies as a function of both the intervention services provided and foster parent characteristics. Studying the effects of foster parent quality can suggest which aspects of child functioning are more or less canalized at various developmental periods. This paper considers salient developmental issues of infancy, preschool years, middle childhood, and adolescence and examines ways in which these issues may present special difficulties for foster children. Across development, foster care is associated with difficulties regulating behaviors, emotions, and physiology. Thus, conditions associated with foster care placement (e.g., disruptions in care, maltreatment) appear to affect very basic and fundamental regulatory processes. Interventions have been designed that target developmentally specific manifestations of regulatory difficulties. Although the literature regarding evidence-based interventions for foster parents is quite limited, preliminary findings provide some evidence that nurturing, responsive care can serve to partially remediate early deficits. These findings suggest that stable and nonfrightening care is essential for normal development. Nonetheless, even in the case of quite adverse early experience that results in problematic child outcomes, there is some evidence that the development of many systems remains relatively plastic.