Child marriage violates girls’ human rights and adversely affects their health and well-being. While age at marriage is increasing in most regions of the developing world, early marriage persists for large populations. Worldwide, it is estimated that more than one out of three women aged 20–24 were married before age 18, and one out of seven were married before age 15. There is great variation in child marriage practices across and within regions and between ethnic and religious groups. Eradicating child marriage has long been on the agenda of the United Nations and of individual countries. Indeed, all countries where child marriage occurs are signatories to international charters and covenants that discourage the practice. Population Council researchers are seeking to prevent child marriage and to support married girls in several countries. These programs include expanding opportunities (education, livelihoods) for girls, especially those most at risk of early marriage, and working directly with gatekeepers (parents, boys/men, religious and community leaders) to remove barriers that prevent girls from accessing those opportunities. The Council’s research demonstrates that successful programs for girls are based on a clear understanding of the local cultural and economic context. Such programs also seek to expand opportunities for girls and limit the constraints to economic empowerment that compel girls and their families to choose early marriage and childbearing.