Population aging was one of the most distinctive events of the 20th century and will remain important throughout the 21st century. Initially, a phenomenon of more developed countries, the process has recently become apparent in much of the developing world as well. The shift in age structure associated with population aging has a profound impact on a broad range of economic, political, and social conditions. This report provides an overview of the world population aging process, focusing on five relevant public policy issues. In dealing with the issues, the report notes the course of the aging process, which has not been the same in all countries. There has been considerable variation in timing, levels, and patterns. The report's assessment of the general trends is disaggregated into development regions and major geographic areas whenever possible. There are five chapters: (1) "Demographic Determinants of Population Ageing" examines the worldwide decline in fertility and mortality that underlies population aging; (2) "The Magnitude and Speed of Population Ageing" explores regional differences in the progression of the aging process through analysis of the percentages and growth rates of the older groups of the population; (3) "The Changing Balance between Age Groups" highlights, from various perspectives, the changes in the relative size of the older and younger groups of the population; (4) "A Demographic Profile of the Older Population" draws attention to two important features of the aging process: the progressive aging of the older population itself and its feminization; and (5) "The Socio-Economic Characteristics of the Older Population" focuses on two dimensions that can greatly affect the well-being of older individuals: labor force participation and literacy. (Contains 40 references and 36 figures. Annex tables include: (1) Definition of the Indicators of Population Ageing"; (2) "Classification of Major Areas and Regions"; and (3) "Profiles of Ageing.") (BT)