The world is in the midst of a significant demographic transition with important implications for the macroeconomic performance of the global economy. This paper summarizes the key features of the current and projected future demographic change that are likely to have macroeconomic effects. It then applies a new ten region global model (an extended version of the MSG-Cubed model) incorporating demographic dynamics, to examine the consequences of projected global demographic change on the world economy from 2005 to 2050. A distinction is made between the effects on each country of its own demographic transition and the effects on each country of the equally large demographic changes occurring in the rest of the world.