The Democratic Party is a liberal political party in the United States. Sitting on the center to center-left of the political spectrum, it is the world's oldest active political party, having been founded in 1828. Its main rival is the Republican Party, and since the 1850s the two have since dominated American politics.

It initially supported Jacksonian democracy, agrarianism, and geographical expansionism, while opposing a national bank and high tariffs. Democrats won six of the eight presidential elections from 1828 to 1856, losing twice to the Whigs. In 1860, the party split into Northern and Southern factions over slavery. The party remained dominated by agrarian interests, contrasting with Republican support for the big business of the Gilded Age. Democratic candidates won the presidency only twice between 1860 and 1908 though they won the popular vote two more times in that period. During the Progressive Era, some factions of the party supported progressive reforms, with Woodrow Wilson being elected president in 1912 and 1916.

In 1932, Franklin D. Roosevelt was elected president after campaigning on a strong response to the Great Depression. His New Deal programs created a broad Democratic coalition which united White southerners, Northern workers, labor unions, African Americans, Catholic and Jewish communities, progressives, and liberals. From the late 1930s, a conservative minority in the party's Southern wing joined with Republicans to slow and stop further progressive domestic reforms. After the civil rights movement and Great Society era of progressive legislation under Lyndon B. Johnson, who was often able to overcome the conservative coalition in the 1960s, many White southerners switched to the Republican Party as the Northeastern states became more reliably Democratic. The party's labor union element has weakened since the 1970s amid deindustrialization, and during the 1980s it lost many White working-class voters to the Republicans under Ronald Reagan. The election of Bill Clinton in 1992 marked a shift for the party toward centrism and the Third Way, shifting its economic stance toward market-based policies. Barack Obama oversaw the party's passage of the Affordable Care Act in 2010.

In the 21st century, the Democratic Party's strongest demographics are urban voters, college graduates (especially those with graduate degrees), African Americans, women, younger voters, irreligious voters, the unmarried and LGBTQ people. On social issues, it advocates for abortion rights, gun control, LGBTQ rights, action on climate change, and the legalization of marijuana. On economic issues, the party favors healthcare reform, paid sick leave, paid family leave and supporting unions. In foreign policy, the party supports liberal internationalism as well as tough stances against China and Russia.

Democratic Party officials often trace its origins to the Democratic-Republican Party, founded by Thomas Jefferson, James Madison and other influential opponents of the conservative Federalists in 1792. That party died out before the modern Democratic Party was organized; the Jeffersonian party also inspired the Whigs and modern Republicans. Historians argue that the modern Democratic Party was first organized in the late 1820s with the election of war hero Andrew Jackson of Tennessee, making it the world's oldest active political party. It was predominately built by Martin Van Buren, who assembled a wide cadre of politicians in every state behind Jackson.

Since the nomination of William Jennings Bryan in 1896, the party has generally positioned itself to the left of the Republican Party on economic issues. Democrats have been more liberal on civil rights since 1948, although conservative factions within the Democratic Party that opposed them persisted in the South until the 1960s. On foreign policy, both parties have changed positions several times.

The Democratic Party evolved from the Jeffersonian Republican or Democratic-Republican Party organized by Jefferson and Madison in opposition to the Federalist Party. The Democratic-Republican Party favored republicanism, a weak federal government, states' rights, agrarian interests (especially Southern planters), and strict adherence to the Constitution. The party opposed a national bank and Great Britain. After the War of 1812, the Federalists virtually disappeared and the only national political party left was the Democratic-Republicans, which was prone to splinter along regional lines. The era of one-party rule in the United States, known as the Era of Good Feelings, lasted from 1816 until 1828, when Andrew Jackson became president. Jackson and Martin Van Buren worked with allies in each state to form a new Democratic Party on a national basis. In the 1830s, the Whig Party coalesced into the main rival to the Democrats.

When exactly the Democratic party formed is still debated among historians, with many putting forth the 1828 date of the creation of a federal structure for the various Jacksonian movements as the foundation date, however, it could also be argued that the foundation of these Jacksonian groups could be the foundation date. In that case the Democratic Party would be formed on December 23, 1823, when the Greensburg Committee read the Greensburg Resolution outside the Westmoreland County Courthouse in Greensburg, Pennsylvania. The committee consisted of five of Greensburg's most prominent political figures, the brothers Jacob M. Wise (state senator), John H. Wise (state representative and brigadier general), and Frederick A. Wise (owner and editor of the Westmoreland Republican), alongside David Marchand (state representative), and James Clarke (state representative). The Greensburg Resolution was the first published call for Jackson to run for President with the committee being the first overtly "Jacksonian" organization, dubbed the 'origin' of the Jackson movement that turned into the Democratic party.