The process of nullification may refer to:

• The legal theory that a U.S. State has the right to nullify, or invalidate, any federal law which that state has deemed unconstitutional. The theory is based on a view that the sovereign States formed the Union, and as creators of the compact hold final authority regarding the limits of the power of the central government. Under this theory, the States and not the Federal Bench determine the extent of the Government's power. Some now consider it a discredited doctrine with no legal basis under U.S. law. (See also: interposition) See the following articles:
  • The Kentucky and Virginia Resolutions were an early statement of this doctrine.
  • The Hartford Convention, in which New England Federalists considered secession from the United States of America.
  • The Nullification Crisis in the United States of America, in which South Carolina passed legislation legalizing its invalidation of objectionable federal laws.

• Jury nullification, a legal term that refers to a jury's right to deliver a verdict in contradiction to written law.
• Body nullification, the practice of removing body parts.
• Physical nullification, a hypothesized process which results when ordinary mass/energy encounters "negative" mass/energy. Not to be confused with annihilation which involves anti-matter.