This chapter examines the relationship between federalism and the EU, tracing the historical and political association between the two and assessing the EU’s unique sovereignSovereign character. It argues that the EU embodies elements of both cooperative and constitutive federalism, combining Member States’ continued autonomy with a shared supranational project. The analysis outlines how the EU’s legal and institutional framework reflects the three core principles of federalFederal order—integrityIntegrity, loyaltyLoyalty, and adjudicationAdjudication—through provisions such as the principles of conferralConferral, subsidiaritySubsidiarity, and respect for national identity, as well as the supremacy of EU law and the protection of EU fundamental values. Drawing on these principles, the chapter explores the dynamic balance of political authorityAuthority between the national and supranational levels, highlighting the EU’s flexibility, political nature, and reliance on consensus. It concludes that federalism provides a suitable analytical framework for understanding the EU’s constitutionalConstitutional structure, its evolving balance of power, and its distinctive model of shared governance.