We share with our brothers and sisters our earliest memories, our parents, our home, our cultural heritage and its values. How has that "accidental bond," formed at birth and tested in our childhood, shaped us as adults? Drawing on detailed interviews with eight sets of adult siblings and integrating research from leading psychologists and social scientists, journalist Susan Scarf Merrell reveals that these relationships forged in childhood influence our lives in often unsuspected and startling ways. No matter what kind of relationships we now have with our siblings - close or distant, loving or hostile - our histories with them exert a profound effect on our current relationships with lovers, friends, coworkers, even our own children. Understanding that bond can give us fresh insights into the adults we have become.