The proportion of older people in the general population is steadily increasing worldwide, with the most rapid growth in low- and middle-income countries. This demographic change is to be celebrated, because it is the consequence of socioeconomic development and better life expectancy. However, population aging also has important implications for society—in diverse areas including health systems, labor markets, public policy, social programs, and family dynamics. A successful response to the aging population will require capitalizing on the opportunities that this transition offers, as well as effectively addressing its challenges.