It is a settled rule of international law that a State may not rely on the provisions of its 'internal law' as justification for failing to comply with international obligations. However, the judiciaries of most countries, including those with a high record of compliance with international norms, have increasingly felt the need to preserve the area of fundamental principles, where the State's inclination to retain full sovereignty seems to act as an unbreakable 'counter-limit' to the limitations deriving from international law. This volume explores this trend by adopting a comparative perspective, addressing the question of how conflicts between international law and national fundamental principles are dealt with and resolved within a specific legal system. The contributing authors identify common tendencies and fundamental differences in the approaches and evaluate the implications of this practice for the future of the principle of supremacy of international law.