Within the study of European integration, the questions of the existence of "social Europe* and the possible impact of European integration on national welfare policies continue to be most disputed. The present study aims to contribute to this scholarly discussion, questioning to what extent the European Union has institutionalised social security rights, how, and with what impact on national welfare policies. Whereas existing research either tends to investigate a process of European integration in its own right or focuses on the impact of European integration, this study employs a two-step research agenda. It attempts to bridge two layers of institutionalisation by, first, analysing the gradual development of Community Regulation 1408/71, which entitles the migrant worker/person to equal and exportable social security rights within the European Union, and, subsequently, by examining how that specific integration process has impacted on Danish and German social security policies and the organising principles behind them. In order to examine the two separate - and intertwined - layers of institutionalisation, a diachronic, process-tracing study is carried out on the basis of the argument that the effective reach, meaning and impact of Community law and policy unfolds gradually over time and through subtle steps at two levels of decisionmaking. The analysis brings into focus institutionalisation through the interaction of law and politics. The European Court of Justice has continuously interpreted the scope and content of the Regulation, and has appeared to act when politics has been absent. Judicial activism, furthering cross-border social security, has been seconded by the European Commission’s persistent attempts to set the agenda. However, the research also finds that institutionalisation has not been progressively driven towards "more Europe', but that politics at times responds, either through collective reactions or through the subsequent national implementation of supranational decisionmaking. The research findings, however, also suggest that such political response may not be the last word, since the Court, on request, may reinterpret matters. On the basis of the analysis of institutionalisation between an extensive T0 and T2, the study concludes that over time the European Union has established a social security dimension, which increasingly has impacted on and restructured the organising principles of national welfare policies, however, not in a systematic, immediate or converging wav.