Preemption is the legal doctrine that a higher source of law can displace or override a lower source of law.
In plain language, if two rules conflict, the higher rule may control. In U.S. law, preemption often refers to federal law overriding state or local law when the Constitution, a statute, or a regulatory scheme gives federal law priority.
Why it matters
Preemption matters because it can decide which legal rule actually governs. A state may create a consumer, employment, safety, or licensing rule, but a federal statute or regulation may limit, override, or leave room for that state rule.
The term is common in regulated industries where several layers of government operate at once.
Where it appears
Preemption appears in constitutional litigation, agency regulation, product-labeling disputes, labor law, banking, transportation, immigration, telecommunications, and consumer-protection cases.
Practical example
A state adopts a product-labeling requirement. A manufacturer argues that federal law already controls the label and leaves no room for a different state requirement. The dispute may turn on preemption.
How it differs from nearby terms
Preemption differs from supremacy clause. The Supremacy Clause is the constitutional source for federal priority; preemption is the doctrine used to analyze displacement in specific disputes.
It also differs from federalism, which describes the broader division of power between federal and state governments.
Related terms
Quick knowledge check
Question: What does preemption usually decide?
Answer: It decides whether a higher legal rule overrides or displaces a lower or conflicting rule.