European Integration is analysed in a historical and in a comparative perspective by applying New Institutional Economics. European Integration is shaped by rules being triggered for further Integration and simultaneously giving integration direction. The analysis starts with the European Coal and Steel Community and ends with the European Union. The functions of rules explain institutionalisation as well as non-institutionalisation of Europe. The influence of these functions varies from country to country and from integration step to integration step. Additionally, these functions can be interrelated in different ways.