Although siblings are a fixture of family life, research on sibling relationships lags behind that on other family relationships. To stimulate interest in sibling research and to serve as a guide for future investigations by family scholars, we review four theoretical psychologically oriented perspectives—(a) psychoanalytic-evolutionary, (b) social psychological, (c) social learning, and (d) family-ecological systems—that can inform research on sibling relationships, including perspectives on the nature and influences on developmental, individual, and group differences in sibling relationships. Given that most research on siblings has focused on childhood and adolescence, our review highlights these developmental periods, but we also incorporate the limited research on adult sibling relationships, including in formulating suggestions for future research on this fundamental family relationship.

This study investigated associations between sibling relationships and adjustment among 179 African American adolescent siblings (controlling for family factors), and tested moderating effects of familism values and birth order. Two-level random intercept models revealed that familism values moderated sibling relationship-adjustment linkages, suggesting that youth who reported both strong familism values and harmonious sibling relationships showed the most positive outcomes. These effects were more consistent for older than for younger siblings. Findings highlight the role of cultural values and birth order in shaping sibling influence processes.