We consider the likely economic impact and prospects for monetary integration among Belarus, Kazakhstan, the Russian Federation and Ukraine as part of the Single Economic Space they have agreed to set up. A monetary union among these countries poses three interesting issues for the structure and process of integration: they have already been members of a wider currency union that collapsed, so it is necessary to handle the problems of history; secondly the union would be of very unequal size with the Russian Federation outweighing the others taken together, so we must consider how the national interests would be balanced; lastly natural resources, particularly oil and gas pose problems for dependence and for the determination of the external exchange rate.