Nullification is the legal and political doctrine that a U.S. state has the authority to declare a federal law unconstitutional and therefore void and unenforceable within its borders. The doctrine rests on a particular reading of the nature of the union between the states and the federal government - specifically, that states retain sovereign authority to judge the limits of federal power. Nullification is distinct from related concepts such as interposition, preemption, and secession, though these are sometimes conflated in popular and political usage.

Nullification in its strictest form holds that individual states, acting through their legislatures or conventions, may refuse to enforce or permit enforcement of federal statutes they deem to exceed Congress's enumerated powers. A softer variant, interposition, holds that states may formally protest or place themselves between their citizens and federal enforcement without claiming outright voidance of federal law. Both doctrines are associated with a compact theory of the Constitution - the view that the Constitution is an agreement among sovereign states, which retain the authority to interpret its limits.

The doctrine is historically associated with the Virginia and Kentucky Resolutions of 1798-1799, authored by James Madison and Thomas Jefferson respectively, and with South Carolina's Nullification Crisis of 1832-1833, in which the state formally declared federal tariff acts null and void within its borders. President Andrew Jackson forcefully rejected the doctrine and Congress passed the Force Act authorizing military enforcement.

The prevailing view among constitutional scholars and the federal judiciary is that nullification is legally invalid. The Supremacy Clause of Article VI establishes federal law as supreme, and the Supreme Court's authority as final arbiter of constitutionality was established in Marbury v. Madison (1803) and affirmed in McCulloch v. Maryland (1819) and Cooper v. Aaron (1958). The Civil War and subsequent constitutional developments are widely cited as historical repudiation of nullification and related doctrines.

Nonetheless, the doctrine recurs in American political life. State-level resistance to federal law has taken various contemporary forms, including state refusal to enforce federal marijuana laws, state non-compliance with certain provisions of the Real ID Act, and sanctuary city policies limiting cooperation with federal immigration enforcement. Proponents argue these represent legitimate exercises of state sovereignty; critics argue they are legally and conceptually distinct from nullification, or that they are nullification under another name.

Scholars disagree about whether the historical record supports the compact theory of the Constitution and whether Madison and Jefferson intended the Virginia and Kentucky Resolutions to endorse nullification as later practiced. A fuller account of this history is available on the History page.

A strong consensus among constitutional law scholars holds that nullification, in its strict form, is not a valid legal doctrine under current federal constitutional interpretation. This consensus is based on the Supremacy Clause, Supreme Court precedent, and post-Civil War constitutional history. Dissenting legal and political arguments exist and are addressed on the Viewpoints pages.

• Compact Theory / Pro-Nullification - The Constitution is a compact among sovereign states, which retain the right to judge federal overreach and refuse enforcement of unconstitutional laws.

• Nationalist Constitutionalism - The Constitution created a supreme federal government whose laws bind states; the Supreme Court, not individual states, is the proper arbiter of constitutionality.

• Interposition as Distinct Doctrine - States may formally resist or slow federal action through interposition short of outright nullification, consistent with federalism and without requiring a claim of sovereignty over constitutional interpretation.

• Pragmatic Federalism / De Facto Non-Enforcement - Whether or not nullification is constitutionally valid, states retain practical and political tools to resist federal policy, and the line between non-enforcement and nullification is not always meaningful in practice.

• Nullification - History
• Nullification - Debate
• Nullification - Legal Consensus
• Federalism
• States' Rights
• Secession
• Supremacy Clause
• Interposition
• Virginia and Kentucky Resolutions
• Nullification Crisis

1. U.S. Constitution, Art. VI, cl. 2 (Supremacy Clause).
2. Marbury v. Madison, 5 U.S. (1 Cranch) 137 (1803).
3. McCulloch v. Maryland, 17 U.S. (4 Wheat.) 316 (1819).
4. Cooper v. Aaron, 358 U.S. 1 (1958).
5. Virginia Resolutions, December 1798; Kentucky Resolutions, November 1798 and November 1799.
6. Proclamation Regarding Nullification, Andrew Jackson, 10 December 1832.
7. Force Act, 2 March 1833, 4 Stat. 632.
8. Andrew C. Lenner, “John Taylor and the Origins of American Federalism,” Journal of the Early Republic 17:3 (1997).
9. Thomas E. Woods Jr., Nullification: How to Resist Federal Tyranny in the 21st Century (2010), for contemporary recurrence of nullification arguments.