EU involvement in healthcare policies is growing, despite the fact that national governments prefer to keep an almost exclusive say in these policies. This article explains how this shift of authority could happen and explores whether it will lead to a European healthcare union. It argues that federalism offers the most fruitful way to do so because of its sensitivity to the EU’s institutional settings and to the territorial dimension of politics. The division of competences and national diversity of healthcare systems have been major obstacles for the formation of a healthcare union. However, the EU obtained a role in healthcare through the impact of non-healthcare legislation, voluntary co-operation, court rulings, governments’ joint-decision traps, and fiscal stress of member states. The emerging European healthcare union is a system of cooperative federalism without much cost-sharing. The healthcare union’s robustness is limited, also because it does not generate much loyalty towards the EU.