Belgium is one of the six founding members of European integration, but it is often seen as a special one. In both policy and research, the country is widely known as the “heart of Europe.” It even sells itself to the outside world in this way. This metaphor has a double meaning, a literal and a figurative one. First, Belgium’s capital, Brussels, qualifies as the unofficial capital of the European Union. This meaning is strongly supported by facts, with the city hosting the most numerous and the most important institutions. The second meaning requires more detailed consideration. Indeed, and second, Belgium is perceived to be the most European of all European countries, even prepared to exchange sovereignty for supranationalism at any time and any price. A closer look at data, decisions, and developments shows, however, that while support for European integration is widespread, it is not omnipresent either in time or in place. Particularly in Flanders, the northern part of the country, support has been less obvious than elsewhere. Indeed, to understand Belgium and/in the European Union, one also has to understand the functioning of Belgium as a federal state composed of communities and regions, thus as a system of multilevel governance. While it is not the only federation among European Union member states, it uniquely combines a wide variety of federal characteristics. Most importantly here, the gradual process of federalization that Belgium has experienced has given the federated entities a strong voice in European Union decision-making. Member states still need to speak with one voice, however, resulting in a complex system of coordination and representation. The possibilities and realities of this system have attracted quite a lot of scholarly interest. The same goes for the rather fundamental question of whether the European Union and federated entities should be seen as unintended partners in the hollowing out of the federal state or whether the opposite holds true and the European Union is coming to Belgium’s rescue. The jury is still out on this, though the answer seems to be growing more and more complex as time passes.