Take a close look at sibling relationships--particularly how siblings navigate power, control, and influence and how the relationship affects the development of the individuals involved. While such relationships are both complementary and reciprocal, they transforms rather dramatically: from hierarchical in early and middle childhood, to egalitarian by early adulthood. This issue to examines: the processes and consequences of such dynamic power shifts for our broader understanding of how these relationship dynamics change and develop throughout the life course, how such dynamics may be similar or different cross-culturally, and how they influence the quality of the sibling relationship, as well as the well-being of youth. To do so, the authors present research from each developmental period from early childhood through young adulthood, as well as cross-cultural research, in order to further understanding of the developmental and contextual themes that allow for drawing broader conclusions. This is the 156th volume in this Jossey-Bass series New Directions for Child and Adolescent Development. Its mission is to provide scientific and scholarly presentations on cutting edge issues and concepts in this subject area. Each volume focuses on a specific new direction or research topic and is edited by experts from that field.