For a club such as the European Union, an important question is when, and under which conditions, a subset of the members should be allowed to form "inner clubs" and enhance cooperation. Flexible cooperation allows members to participate if and only if they benefit, but it generates a freerider...

Does European economic integration create more inequality between domestic regions, or is the opposite true? We show that a general answer to this question does not exist, and that the outcome depends on the liberalisation scenario. In order to examine the impact of European and international...

In many organizations, decisions are taken by unanimity giving each member veto power. We analyze a model of an organization in which members with heterogenous productivity privately contribute to a common good. Under unanimity, the least efficient member imposes her preferred effort choice on...

Should a subset of member states of a federation be allowed to form a sub-union on some policy issue? When centralization is not politically feasible, allowing an enhanced cooperation agreement among a subset of countries permits the latter to gain benefits which would otherwise be lost....

Around the world many countries are about to break apart, stay together, join in federations or build supranational organisations. The political debate of the European constitution is embedded in this context. The question arises which policies have to be shifted to the central European level...