What is the supreme law of the land?
In the United States of America, the Constitution is the supreme law of the land. No state or local law or ordinance can take precedence over the Constitution’s provisions. Article VI of the Constitution states as follows:
“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, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.”
While the Constitution is the supreme law in the United States, its main provisions, especially the first ten amendments to the original document, known as “the Bill of Rights,” remain subject to interpretation. The supremacy of the Constitution, however, remains unchallenged. This is important because individual state legislatures occasionally pass laws that are later found by the Supreme Court of the United States to contravene the Constitution’s provisions—at least as those provisions are interpreted at any given moment. A prominent example of this involves the politically divisive issue of abortion. The state of Missouri has passed legislation in the past intended to make it more difficult for women to abort a pregnancy. Conversely, carefully phrased, repeated Supreme Court rulings have found Missouri’s attempts at blocking abortions to be unconstitutional in light of the famous 1973 Roe v. Wade case that legalized the medical procedure.
If you are asking about the United States, the answer is that the supreme law of the land is the Constitution of the United States. This is laid out in Article VI of the Constitution itself. Part of that article says that
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof … shall be the supreme Law of the Land…
What this means is that no law made by any state, or even by the Congress of the United States, can contradict the Constitution.
This is why the Supreme Court of the United States is able to overturn laws by declaring them to be unconstitutional. Those laws are, the Court says, contrary to the Constitution. Since the Constitution is the supreme law of the land, those laws cannot be valid and must be overturned.
So, the Constitution of the United States is the supreme law of the land, meaning that no law can be legal if it contradicts what the Constitution says.