Errors in projecting demographic change have been considerable in recent decades. The fertility declines and increased longevity associated with the concluding global demographic transition have been surprisingly rapid, leading to accelerated ageing of populations in developed countries and in several advanced developing countries. This paper introduces a global demographic model for the analysis of these changes, from which emerge their implications for population sizes, age distributions and gender compositions. From these results are inferred corresponding changes in labour force size and in patterns of consumption and saving which are then analysed using a global economic model in which regional households are disaggregated into eight components comprising four age groups and two genders. Demographic change is found to act most significantly through variations across age groups in savings behaviour and its effects on aggregate savings and investment and their international distribution. Corresponding variation in labour force participation is also significant, acting through labour supply growth and the pattern of comparative advantage. Secondary effects arise from variations in consumption preferences across age groups.