This paper analyzes macroeconomic effects of projected population aging in industrial countries. The effects of population aging are examined with a theoretical model and simulations of the IMF's multiregion econometric model (MULTIMOD). The study highlights that an older population will consume more of aggregate disposable income, require higher government expenditure, and decrease labor supply. These effects should raise real interest rates and lower capital stock and output. Effects on current balances will depend on the relative speed and extent of aging.