© Federico Fabbrini 2017. The chapter argues that Brexit compels the EU institutions and the Member States to engage in constitutional change at EU level. Several provisions of the EU treaties and quasi-constitutional EU norms will need to be amended to adapt to the reality of a Union of twenty-seven. The revision of these legal norms, however, may provide an opportunity to discuss radical changes to the EU constitutional system-a prospect that had been discussed during the euro-crisis, and in the context of the celebrations for the 60th anniversary of the Rome Treaties Treaty reform in the EU has been mixed, and there are many obstacles toward a new constitutional settlement in Europe. Nevertheless, the growing calls for a multispeed Europe signal a credible alternative: after Brexit, integration by a sub-group of states remains a distinctive possibility in case the efforts to reform the EU constitutional system should falter got idiosyncratic national reasons.