This chapter aims at assessing the impact of the European integration on the political institutions of federal Belgium. Over the last 50 years, Belgian federal political institutions witnessed, in parallel, a pooling of their sovereignty to the EU level and a process of decentralization at the domestic level. Indeed, in EU federal Member States like Belgium, while some competences are highly Europeanized - e.g. agriculture, environment - they are, at the same time, regionalized or shared between the regional and national governance levels. This situation raises numerous questions, among which how are regional and national institutions in federal countries shaped by the multi-level setting in which they operate? Against this background, the chapter tackles the following question: how does Europeanization affects Belgian federal political institutions? In particular, the chapter analyses and compares the direct and indirect consequences of the European integration on both executive (i.e. government and their administration) and legislative (i.e. regional and national parliaments) institutions. It discusses whether acting within a multi-level setting triggers, on the one hand, a rise of the degree of centralization and cooperation between political institutions or, on the other hand, whether it stimulates pressure for more decentralization. In fine, the chapter contributes to the literature on the differentiated impact of European integration as well as on federal studies.