The Pony Express was an American express mail service that used relays of horse-mounted riders. It operated from April 3, 1860, to October 26, 1861, between Missouri and California. It was operated by the Central Overland California and Pikes Peak Express Company.

During its 18 months of operation, the Pony Express reduced the time for messages to travel between the east and west US coast to about 10 days. It became the west's most direct means of east–west communication before the first transcontinental telegraph was established (October 24, 1861), and was vital for tying the new U.S. state of California with the rest of the United States.

Despite a heavy subsidy, the Pony Express was not a financial success and went bankrupt in 18 months, when a faster telegraph service was established. Nevertheless, it demonstrated that a unified transcontinental system of communications could be established and operated year-round. When replaced by the telegraph, the Pony Express quickly became romanticized and became part of the lore of the American West. Its reliance on the ability and endurance of hardy riders and fast horses was seen as evidence of rugged American individualism of the frontier times.