Between 2015 and 2050 world population is projected to increase by nearly 2.5 billion, rising from 7.3 billion to an estimated 9.8 billion. The vast majority of that projected increase—an estimated 97 percent—will occur in the developing world. Demography is not destiny, but population growth in the developing world is a challenge‐multiplier. In recent decades, notable gains have been made in reducing the incidence of hunger and poverty in the world, but progress has been slow in countries with high fertility rates. The nations with the fastest growing populations tend to rank high on global indices of hunger, poverty, environmental degradation, and fragility; and many of these countries face enormous obstacles to economic development in the form of climate change, regional or ethnic conflict, or water scarcity. Most of these countries also have large numbers of unemployed young people between the ages of 15–24, a demographic factor that can contribute to, or exacerbate, political instability and conflict. Unless fertility rates in these countries fall faster than currently anticipated by demographers, many of these countries face an uncertain future. Lack of progress in improving living conditions in these countries could lead to greater political instability and conflict and increase the growing number of refugees and internally displaced persons in the world.