Anti-Federalists, in American history, opponents of the adoption of the federal Constitution. Leading Anti-Federalists included George Mason, Elbridge Gerry, Patrick Henry, and George Clinton. Later, many of the Anti-Federalists opposed the policies of the Federalist party and of Alexander Hamilton.

U.S. leaders who opposed the strong central government envisioned in the Constitution of the United States of 1787. Their agitation led to the creation of the Bill of Rights. While admitting the need for changes in the Articles of Confederation, they feared that a strong federal government would infringe on states' rights. The group's adherents, including George Mason, Patrick Henry, Thomas Paine, Samuel Adams, and George Clinton, were as numerous as the members of the Federalist Party, but their influence was weak in urban areas, and only Rhode Island and North Carolina voted against ratification of the Constitution. Anti-Federalists were powerful during the presidency of Thomas Jefferson, when they formed the nucleus of what later became the Democratic Party.

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