The Constitution Party, named the U.S. Taxpayers' Party until 1999, is an ultra-conservative political party in the United States that promotes a religiously conservative interpretation of the principles and intents of the United States Constitution. The party platform is based on originalist interpretations of the Constitution and shaped by principles which it believes were set forth in the Declaration of Independence, the Bill of Rights, the Constitution and the Bible.

The party was founded by Howard Phillips, a conservative activist, after President George H. W. Bush violated his pledge of "read my lips: no new taxes". During the 1992 and 1996 presidential elections, the party sought to give its presidential nomination to prominent politicians including Pat Buchanan and Ross Perot, but was unsuccessful and instead selected Phillips as its presidential nominee in three successive elections. Michael Peroutka was given the presidential nomination in 2004, followed by Chuck Baldwin in 2008 (although he faced opposition from multiple state affiliates), Virgil Goode in 2012, Darrell Castle in 2016, Don Blankenship in 2020 and Randall Terry in 2024.

In 2000, Rick Jore, a three-term Republican member of the Montana House of Representatives, became the first member of the party to hold a seat in a state legislature. He was defeated in the 2000, 2002 and 2004 elections; however, he was elected to a state legislature in 2006, the first Constitution Party candidate to be elected. In 2002, Greg Moeller became the first member of the party to win a partisan election. The Constitution parties of Minnesota and Colorado have both achieved major party status once.

As of June 2024^[update], the Constitution Party has 28 members who have been elected to city council seats and other municipal offices across the United States. In terms of registered members, the party ranks fifth among national parties in the United States.

During the 1988 presidential election, Republican nominee George H. W. Bush stated "read my lips: no new taxes" at the 1988 Republican National Convention. However, Bush violated that pledge during his presidency. Following the breaking of the no new taxes pledge, Howard Phillips announced that he would form a third political party called the U.S. Taxpayers' Party.

Phillips formed his new party through the U.S. Taxpayers Alliance, an organization he had founded and which had affiliates in twenty-five states, using its mailing list to announce the formation of a new party. Phillips also attempted to create a coalition with state affiliates of the American Party, but was rejected. The party was accepted into the Coalition for Free and Open Elections alongside the Freedom Socialist Party. The party launched its first petition drive when Jack Perry started a campaign to appear on the 1991 United States special election ballot in Pennsylvania.

From January 25 to 26, 1997, the national committee of the U.S. Taxpayers' Party convened in Miami, Florida. During their meeting it was proposed to change the name of the party to either "Constitutional" or "Independent American", but the vote was tied 27 to 27 so U.S. Taxpayers' was retained as the party's name. In March 1999, another name change was proposed, with American Independent, American Heritage, Constitutional, Independent American, and American Constitution as possible names, but it was unsuccessful. On September 3, 1999, the national convention of the U.S. Taxpayers' Party was held and during it the name of the party was successfully changed to Constitution. Every state affiliate of the party, except for Nevada and California, changed their names except for in Michigan where the Michigan Secretary of State denied the request. The party is still called the U.S. Taxpayers' Party in Michigan as of 2022.

In 1998, Patricia Becker, the U.S. Taxpayer's nominee for Minnesota state auditor, received over 5% of the popular vote giving the U.S Taxpayers' Party major party status in Minnesota. The party would later hold caucuses during the 2000 presidential election.