European integration can no longer be understood as a west European experiment mainly focused on functional and economic policy cooperation. The issues addressed include security and defence, as well as core concerns of European society. This volume explores three interlocking dimensions of integration; functional, territorial, and affiliational. Each dimension influences how countries across the continent engage with European integration. This first volume in the One Europe or Several? series identifies the agenda of a research programme, funded by the British Economic and Social Research Council.