This text deals with the economic analysis of the consequences of demographic change, with special emphasis on the diverging population developments in an interdependent world economy. The global divergence in demographic developments gives rise to a myriad of economic and ethical problems. This topic is treated using the mathematical apparatus of neoclassical optimal growth models. The author tries to disentangle the basic policy issues of a demographically divided world, such as a selective immigration policy, sustainable patterns of international lending and borrowing, development aid and dynamic optimal taxation.