The Whig Party was a mid-19th century political party in the United States. Alongside the Democratic Party, it was one of two major parties from the late 1830s until the early 1850s and part of the Second Party System. As well as four Whig presidents (William Henry Harrison, John Tyler, Zachary Taylor, and Millard Fillmore), other prominent members included Henry Clay, Daniel Webster, Rufus Choate, William Seward, John J. Crittenden, and John Quincy Adams (whose presidency ended prior to the formation of the Whig Party). The Whig base of support was amongst entrepreneurs, professionals, Protestant Christians (particularly Evangelicals), the urban middle class, and nativists. It had much less backing from poor farmers and unskilled workers.

The party was hostile towards the ideology of "manifest destiny", territorial expansion into Texas and the Southwest, and the Mexican–American War. It disliked presidential power, as exhibited by Andrew Jackson and James K. Polk, and preferred congressional dominance in lawmaking. Members advocated modernization, meritocracy, the rule of law, protections against majority rule, and vigilance against executive tyranny. They favored an economic program known as the American System, which called for a protective tariff, federal subsidies for the construction of infrastructure, and support for a national bank. The party was active in both the Northern and Southern United States and did not take a firm stance on slavery, but Northern Whigs tended to be less supportive than their Democratic counterparts.

The Whigs emerged in the 1830s in opposition to U.S. president Andrew Jackson, pulling together former members of the National Republican Party, the Anti-Masonic Party, and disaffected Democrats. The Whigs had some weak links to the defunct Federalist Party, but the Whig Party was not a successor to that party, and many Whig leaders, including Henry Clay, had aligned with the rival Democratic-Republican Party. In the 1836 presidential election, four different Whig candidates received electoral votes, but the party failed to defeat Jackson's chosen successor, Martin Van Buren. Whig nominee William Henry Harrison unseated Van Buren in the 1840 presidential election but died one month into his term. Harrison's successor, John Tyler, a former Democrat, broke with the Whigs in 1841 after clashing with Clay and other party leaders over economic policies such as the re-establishment of a national bank.

Clay clinched his party's nomination in the 1844 presidential election but was defeated by Democrat James K. Polk, who subsequently presided over the Mexican–American War. Whig nominee Zachary Taylor won the 1848 presidential election, but Taylor died in 1850 and was succeeded by Millard Fillmore. Fillmore, Clay, Daniel Webster, and Democrat Stephen A. Douglas led the passage of the Compromise of 1850, which helped to defuse sectional tensions in the aftermath of the Mexican–American War for a time. Nonetheless, the Whigs suffered a decisive defeat in the 1852 presidential election partly due to sectional divisions within the party. The Whigs collapsed following the passage of the Kansas–Nebraska Act in 1854, with most Northern Whigs eventually joining the anti-slavery Republican Party and most Southern Whigs joining the nativist American Party and later the Constitutional Union Party. The last vestiges of the Whig Party faded away after the start of the American Civil War, but Whig ideas remained influential for decades. During the presidency of Abraham Lincoln, ex-Whigs dominated the Republican Party and enacted much of their American System. Presidents Abraham Lincoln, Rutherford B. Hayes, Chester A. Arthur, and Benjamin Harrison were Whigs before switching to the Republican Party, from which they were elected to office. It is considered the primary predecessor party of the modern-day Republicans.

During the 1790s, the first major U.S. parties arose in the form of the Federalist Party, led by Alexander Hamilton, and the Democratic-Republican Party, led by Thomas Jefferson. After 1815, the Democratic-Republicans emerged as the sole major party at the national level but became increasingly polarized. A nationalist wing led by Henry Clay favored policies such as the Second Bank of the United States and the implementation of a protective tariff. A second group, the Old Republicans, opposed these policies, favoring a strict interpretation of the Constitution and a weak federal government.

In the 1824 presidential election, Speaker of the House Henry Clay, Secretary of the Treasury William H. Crawford, Secretary of State John Quincy Adams, and General Andrew Jackson all sought the presidency as members of the Democratic-Republican Party. Crawford favored state sovereignty and a strict constructionist view of the Constitution, while Clay and Adams favored high tariffs and the national bank; regionalism played a central role, with Jackson strongest in the West. Jackson won a plurality of the popular and electoral vote in the 1824 election, but not a majority. The House of Representatives had to decide. Speaker Clay supported Adams, who was elected as president by the House, and Clay was appointed Secretary of State. Jackson called it a "corrupt bargain".

In the years following the 1824 election, former members of the Democratic-Republican Party split into hostile factions. Supporters of President Adams and Clay joined with many former Federalists such as Daniel Webster to form a group informally known as the "Adams party". Meanwhile, supporters of Jackson, Crawford, and Vice President John C. Calhoun joined in opposing the Adams administration's nationalist agenda, becoming informally known as "Jacksonians". Due in part to the superior organization (by Martin Van Buren) of the Jacksonians, Jackson defeated Adams in the 1828 presidential election, taking 56 percent of the popular vote. Clay became the leader of the National Republican Party, which opposed President Jackson. By the early 1830s, the Jacksonians organized into the new Democratic Party.

Despite Jackson's decisive victory in the 1828 election, National Republicans initially believed that Jackson's party would collapse once Jackson took office. Vice President Calhoun split from the administration in 1831. Still, differences over the tariff prevented Calhoun's followers from joining the National Republicans. Meanwhile, the Anti-Masonic Party formed following the disappearance and possible murder of William Morgan in 1826. The Anti-Masonic movement, strongest in the Northeast, gave rise to or expanded the use of many innovations which became an accepted practice among other parties, including nominating conventions and party newspapers. Clay rejected overtures from the Anti-Masonic Party, and his attempt to convince Calhoun to serve as his running mate failed, leaving the opposition to Jackson split among different leaders when the National Republicans nominated Clay for president.