The entrance of ten new members to the European union on May 1st 2004 represents a sizeable political and institutional challenge for the Union. One dimension of this challenge is a source of worry to the different populations of the Union: the economic and financial dimension. The economic advantages for the new members will be considerable. For existing members they will, at best, be modest. The Union will have to bear the increased costs of bringing the economies of future members up to par with those of existing members. In a manner which is both clear and concise, the author analyses how the costs and advantages might be shared out over time among member States and points out the regions and business sectors which will win or lose in the process of integration.