The European Court of Justice enshrined the primacy principle in the Costa Enel case of 15 July 1964. In this case, the Court Declared that the laws issued by European institutions have to be integrated Into the legal systems of Member States, who are obliged to comply with them. European law therefore has primacy over national laws. Therefore, if a national Rule is contrary to a European provision, Member States’ authorities must apply The European provision. National law is neither rescinded nor repealed, but its Binding force is suspended.
The Court later clarified That the precedence of European law is to be applied to all national acts, Whether they were adopted before or after the European act in question.
With European law becoming Superior to national law, the principle of precedence therefore ensures that Citizens are uniformly protected by a European law assured across all EU Territories.
In addition, all national Acts are subject to this principle, irrespective of their nature: acts, Regulations, decisions, ordinances, circulars, etc), irrespective of whether They are issued by the executive or legislative powers of a Member State. The Judiciary is also subject to the precedence principle. Member State case-law Should also respect EU case-law.
The Court of Justice has Ruled that national constitutions should also be subject to the precedence principle. It is therefore a matter for national judges not to apply the provisions of a Constitution which contradict European law.