The United States Postal Service (USPS) is an independent agency of the United States government responsible for providing postal service in the United States. It is one of the few government agencies explicitly authorized by the United States Constitution. Within the United States, it is commonly referred to as the "Post Office", "Postal Service", or "U.S. Mail".

Though postal services have existed on American territory before the United States' establishment, the USPS's first incarnation was established by Benjamin Franklin in Philadelphia in 1775 by decree of the Second Continental Congress. The Post Office Department was created from Franklin's operation in 1792 as part of the United States Cabinet, then was transformed into its current form in 1983 under the Postal Reorganization Act.

Since its reorganization into an independent organization, the USPS has become self-sufficient and has not directly received taxpayer-dollars since the early 1980s with the minor exception of subsidies for costs associated with the disabled and overseas voters. However it is currently borrowing money from the U.S. Treasury to pay its deficits.[3] The decline of mail volume due to increased usage of e-mail has forced the postal service to look to other sources of revenue while cutting costs to maintain this financial balance.[4]

Employing 596,000 workers and over 218,000 vehicles, it is the second-largest civilian employer in the United States (after Wal-Mart) and the operator of the largest civilian vehicle fleet in the world.[5] The USPS is obligated to serve all Americans, regardless of geography, at uniform price and quality. It has exclusive access to letter boxes marked "U.S. Mail." It competes against private package delivery services who cannot deliver to letter boxes and must leave packages by front doors if no one is available to receive them.