The Libertarian Party (LP) is a libertarian political party in the United States that promotes civil liberties, non-interventionism, laissez-faire capitalism, and limiting the size and scope of government. The world's first explicitly libertarian party, it was conceived in August 1971 at meetings in the home of David F. Nolan in Westminster, Colorado, and was officially formed on December 11, 1971, in Colorado Springs. The organizers of the party drew inspiration from the works and ideas of the prominent Austrian school economist Murray Rothbard. The founding of the party was prompted in part due to concerns about the Nixon administration's wage and price controls, the Vietnam War, conscription, and the introduction of fiat money.

The party generally supports a classical liberal platform, much different from the Democratic Party's modern liberalism and progressivism and the Republican Party's conservatism and right-wing populism. Gary Johnson, the party's presidential nominee in 2012 and 2016, claims that the Libertarian Party is more socially liberal than Democrats, and more fiscally conservative than Republicans. Its fiscal policy positions include lowering taxes and abolishing the Internal Revenue Service (IRS), decreasing the national debt, allowing people to opt out of Social Security, and eliminating the welfare state, in part by utilizing private charities. Its social policy positions include ending the prohibition of illegal drugs, advocating criminal justice reform, supporting same-sex marriage, ending capital punishment, and supporting the right to keep and bear arms.

As of May 2024, it is the third-largest political party in the United States by voter registration. In the 2020 election, the Libertarians gained a state legislative seat in the Wyoming House of Representatives, the first such win for the party since 2000. The first and only Libertarian in the United States Congress was Justin Amash, who joined the Libertarian Party in 2020 and left the U.S. House of Representatives in 2021 after choosing not to seek re-election.

In 2022, the Mises Caucus (LPMC) became the dominant faction on the Libertarian National Committee, leading to internal conflicts and significant policy changes, such as regarding immigration and abortion. Some classical liberalism-minded dissidents split from the Libertarian party to form the Association of Liberty State Parties.