This book addresses systematically and quantitatively the role of educational attainment in global population trends and models. By adding education to the traditional demographic characteristics of age and sex, this distinguishing feature substantially alters the way we look at changes in populations and how we project them into the future. In most societies, particularly during the process of demographic transition, women with more education have fewer children, both because they want fewer and because they find better access to birth control. And better educated men and women in virtually all societies have lower mortality rates and their children have a better chance of survival. Migration flows also differ by level of education, and better educated migrants integrate more easily into receiving societies. These pervasive demographic differentials by level of education matter greatly for population dynamics. When we explicitly address this important source of population heterogeneity the projected future population trends are different from those based on the conventional stratifications that include only age and sex. In addition, the future educational attainment levels of the adult population are of great interest in their own right as a key determinant of outcomes ranging across economic growth, quality of governance, and adaptive capacity to environmental change. Traditionally in demography, the sex of a person is considered the most fundamental characteristic because it is essential for studying the process of reproduction. Mortality and migration also show significant variation by gender. Age is another key characteristic because it is the main driver of biological maturation at an early age and is directly related to school attendance, labour force entry, and retirement, all landmarks that are important for social institutions. Because there are distinct age-related patterns of fertility, mortality, and migration intensities, gender and age are considered the most fundamental demographic dimensions. In addition, demographers frequently take into account other biological, social, and economic characteristics, including place of residence (especially urban or rural), citizenship, marital status, race, migration status, employment status, health/disability status, and educational attainment. These additional characteristics are not systematically considered in every study, but tend to appear in corresponding topical studies.