The Third Amendment to the United States Constitution is a part of the Bill of Rights and was introduced in Congress in 1789 by James Madison in response to Anti-Federalist objections to the new Constitution. The amendment places restrictions on the quartering of soldiers in private homes without the owners consent, forbidding the practice in peacetime. The text of the amendment is as follows: "No Soldier shall, in time of peace be quartered in any house, without the consent of the Owner, nor in time of war, but in a manner to be prescribed by law".

The Third Amendment is among the least cited sections of the U.S. Constitution, and to date, no major Supreme Court decision has used the amendment as its primary basis. However, the Third Amendment has been invoked in a few instances as helping establish an implicit right to privacy in the Constitution. Justice William O. Douglas used the amendment along with others in the Bill of Rights as a partial basis for the majority decision in Griswold v. Connecticut (1965), which cited the Third Amendment as implying a belief that an individuals home should be free from agents of the state.