Pork barrel (or pork barrel politics) is a derogatory term used to describe government spending that is intended to enrich constituents of a politician in return for their political support, either in the form of campaign contributions or votes. Typically it involves funding for government programs whose economic or service benefits are concentrated but whose costs are spread among all taxpayers. Public works projects and agricultural subsidies are the most commonly cited examples, but do not exhaust the possibilities. Often allocated through last-minute additions to appropriations bills, pork barrel spending contributes significantly to government deficits.

One of the earliest examples of pork barrel politics in the United States was the Bonus Bill of 1817, which was introduced by John Calhoun to construct highways linking the East and South of the United States to its Western frontier using the earnings bonus from the Second Bank of the United States. Calhoun argued for it using general welfare and post roads clauses of the United States Constitution. Although he approved of the economic development goal, President James Madison vetoed the bill as unconstitutional. Since then, however, U.S. presidents have seen the political advantage of pork barrel politics.

In recent years, a famous pork barrel project is the Interstate 99 designation that was written into law by Pennsylvania Representative Bud Shuster. The number was disputed by road scholars, who envisioned it as a number for a new freeway running along the Atlantic coast. I-99's location is a violation of the Interstate system's numbering rules, as it's located west of Interstate 81, and seven other Interstates whose numerical value is less than 99.

The term is derived from the notion of the government giving every voter a barrel of pork (smoked pork products were, at one time, shipped in barrels).