Definition
The Supremacy Clause appears in Article VI of the U.S. Constitution. It declares that the Constitution, federal statutes, and treaties made under federal authority are the supreme law of the land, binding judges in every state.
In practical terms, the clause settles a conflict-of-laws problem: when a valid federal law and a state law point in different directions, the federal law wins. It is the constitutional foundation for the entire structure of American federalism.
Why it matters
How it works
When a court reviews a clash between federal and state law, it first asks whether the federal law is a valid exercise of an enumerated power. If it is, the court then examines whether Congress intended to preempt state action.
Preemption can be express, stated outright in the statute, or implied, inferred when federal regulation is so pervasive that it occupies the field or when compliance with both laws is impossible. Where the federal law is invalid, the Supremacy Clause does not protect it, and the state law may stand instead.