The populations of many regions are rapidly growing older. The process of population aging is a major success story, which began unfolding only at the end of the twentieth century. Demographers define population aging as an increasing median age of a population or an alteration in the age structure of a population, so that elderly persons are increasingly represented within a country's overall age structure. The economic and social consequences of aging are considerable, particularly with regard to the increasing burden of dependency. These consequences in the industrialized nations of Europe and North America have been well publicized. However, less is known about the effects in less well developed regions. Older populations in many developing countries are growing more rapidly than are those of industrialized nations. Awareness of issues concerning older populations remains low in many nations, even as the absolute numbers of the aged double and triple. In this Data Watch I discuss demographic projections of population aging throughout the world. These projections suggest that developing countries are aging much faster than industrialized countries did, as a result of rapid declines in fertility and broad diffusion of medical knowledge. These countries will be faced with “old” demographic profiles at much lower levels of per capita income than will be true for industrialized nations. 3 In Belgium, for example, it took more than 100 years for the share of the population over age sixty to double from 9 percent to 18 percent. In China the same transition will take only thirty-four years; in Venezuela, only twenty-two years.