Pony Express, in United States history, a mail service in the West, 1860–61. Using relays of riders and horses, the Pony Express provided mail delivery between St. Joseph, Missouri, and Sacramento, California, a distance of 1,966 miles (3,164 km). The Pony Express was operated by the stagecoach firm of Russell, Majors and Waddell. The company was seeking to win a mail contract from the U.S. Post Office by demonstrating that mail could be delivered to California faster by a central route than by the southern route then being used by the Butterfield line. The cost was originally five dollars per half ounce (14 g); it was eventually reduced to one dollar.

The first trip, in April, 1860, took slightly less than 10 days. Horses were changed at stations every 10 to 15 miles (16 to 24 km) and riders every 75 to 100 miles (120 to 160 km). The completion of the cross-country telegraph in October, 1861, made the Pony Express obsolete. It went out of business on October 26, after having made 308 runs each way.