Municipal law is the national, domestic, or internal law of a sovereign state defined in opposition to international law. Municipal law includes not only law at the national level, but law at the state, provincial, territorial, regional or local levels. While, as far as the law of the state is concerned, these may be distinct categories of law, international law is largely uninterested in this distinction and treats them all as one. Similarly, international law makes no distinction between the ordinary law of the state and its constitutional law.
Article 27 of the Vienna Convention on the Law of Treaties provides that, where a treaty conflicts with a state's municipal law (including the state's constitution), the state is still obliged to meet its obligations under the treaty. The only exception to this rule is provided by Article 46 of the Vienna Convention, where a state's expression of consent to be bound by a treaty was a manifest violation of a "rule of its internal law of fundamental importance".
- The Vienna Convention on the Law of Treaties. Accessed 8 February 2007.
- Reydams, Luc Universal Jurisdiction: International and Municipal Legal Perspectives, (Oxford Monographs in International Law), (Oxford University Press, 2004) ISBN 978-0-19-927426-0.