This chapter puts the developed theory to the test. First, after outlining the most important case law of the CJEU on the relationship between EU and Member State law, which has introduced primacy of EU law (also over Member State constitutional law) and the doctrine of direct effect, this chapter also displays the most important judgments by Member State constitutional courts generally holding that there are limits to the primacy of EU law. After analyzing the most important theoretical conceptions and doctrines in literature addressing the difference between the CJEU and the Constitutional Courts of some Member States, this chapter shows how consent-based monism can provide for relief. According to consent-based monism, the EU is the larger circle with regard to its Member States. All EU Member States in turn are independent smaller circles which are also part of the EU circle. The EU competence regime is decisive in this regard. It is vital to pinpoint exactly which competences have been shifted to the European level. According to consent-based monism, an “integration resistant core” must not violate any consensus that has been obtained at the level of the larger EU circle. The larger circle must not autonomously add competences without authorization by all of the smaller circles.