In this pioneering study, Alter demonstrates her mastery of both European law and the politics of law. She demonstrates that Europe's development of a supranational legal system, which has gone far beyond the limited original design of the European Court of Justice (ecj), has become a key vehicle for European integration. Particularly critical were decisions that established the related principles of the "direct effect" of European legal provisions and the supremacy of European over national law. In short, these rulings made it illegal for states to enact laws or policies that contradict European legal obligations. Thus the ecj can use national courts to enforce European law in the national realm. In turn, European law is increasingly brought into national political debates by parties, politicians, and interest groups, which all use it to bolster their own positions. Alter's book demonstrates the resilience of European integration and the comparative strengths and weaknesses of the European legal system. As she concludes, "knowing the position of the European Court of Justice has become as important as knowing the position of member states."