United States Constitution

Article II(2): [The president] shall have power, by and with the advice and consent of the Senate, to make treaties, provided two thirds of the Senators present concur …

Article VI: …This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding….

Restatement (Third) of Foreign Relations Law of the United States (1987)

Para. 111: International Law and Agreements as Law of the United States

(1) International law and international agreements of the United States are law of the United States and supreme over the law of the several States.

(2) Cases arising under international law or international agreements of the United States are within the Judicial Power of the United States and, subject to Constitutional and statutory limitations and requirements of justiciability, are within the jurisdiction of the federal courts.

(3) Courts in the United States are bound to give effect to international law and to international agreements of the United States, except that a “non-self-executing” agreement will not be given effect as law in the absence of necessary implementation.

(4) An international agreement of the United States is “non-self-executing”

(a) if the agreement manifests an intention that it shall not become effective as domestic law without the enactment of implementing legislation,

(b) if the Senate in giving consent to a treaty, or Congress by resolution, requires implementing legislation, or

(c) if implementing legislation is constitutionally required.

Comment (d) International law and agreements as supreme federal law. Treaties made under the authority of the United States, like the Constitution itself and the laws of the United States, are expressly declared to be “supreme Law of the Land” by Article VI of the Constitution. International agreements of the United States other than treaties (see § 303), and customary international law, while not mentioned explicitly in the Supremacy Clause, are also federal law and as such are supreme over State law. Interpretations of international agreements by the United States Supreme Court are binding on the States. Customary international law is considered to be like common law in the United States, but it is federal law. A determination of international law by the Supreme Court is binding on the States and on State courts.

Comment (h) Self-executing and non-self-executing international agreements. In the absence of special agreement, it is ordinarily for the United States to decide how it will carry out its international obligations. Accordingly, the intention of the United States determines whether an agreement is to be self-executing in the United States or should await implementation by legislation or appropriate executive or administrative action. If the international agreement is silent as to its self-executing character and the intention of the United States is unclear, account must be taken of any statement by the President in concluding the agreement or in submitting it to the Senate for consent or to the Congress as a whole for approval, and of any expression by the Senate or by Congress in dealing with the agreement… Whether an agreement is or is not self-executing in the law of another state party to the agreement is not controlling for the United States.