In the post-Maastricht era, member states of the European Union (EU) have proved increasingly reluctant to transfer further competences to the supranational level and are willing to safeguard their sovereignty. Though the responses to the contemporary multiple crises – related to economic and monetary policy, borders and migrations, or democracy and the rule of law – have brought about conflicts over values and sovereignty losses surrounding the legal, economic and political legitimacy of the EU. Against this backdrop, we argue that beyond the traditional contentious (re)distribution of competences between nation-states (national sovereignty) and the EU (and its embryonic forms of supranational sovereignty), new conflicts of sovereignty involve two other key types of sovereignty belonging to the democratic tradition, namely parliamentary sovereignty and popular sovereignty. This introductory article proposes a common analytical framework in order to investigate conflicts in their multi-dimensionality.