This thematic issue examines two main research questions: What are the features, the determinants, and the implications of fiscal integration in a system of multilevel governance like the EU? And, what can the post-pandemic EU learn from established federations when it comes to fiscal integration? We attempt to conceptualize the patterns of EU fiscal integration. In so doing, we identify eight instruments of fiscal integration in a federal or multilevel polity, equally divided between fiscal capacity and fiscal regulation, depending on the side of the budget and the mode of integration (autonomous or dependent). For instance, as part of the fiscal capacity instrument of integration, we propose to distinguish between revenue and expenditure capacity. Revenue capacity is then further divided into tax capacity, based on EU/federal taxes, and budgetary capacity, based on non-independent sources, for instance, contributions from the member states. Expenditure capacity is divided into autonomous spending capacity, meaning direct spending by the EU, and a dependent transfer capacity, where the EU merely distributes resources (both grants and loans) to the member states.