The Pony Express was a fast mail service crossing the North American continent from St. Joseph, Missouri, to Sacramento, California, from April 1860 to October 1861. It became the west's most direct means of east-west communication before the telegraph and was vital for tying California closely with the Union just before the American Civil War.

The Pony Express was a mail delivery system of the Leavenworth & Pike's Peak Express Company of 1849 which in 1850 became the Central Overland California & Pike's Peak Express Company. This firm was founded by William H. Russell, Alexander Majors, and William B. Waddell.

The original fast mail services had messages carried by horseback riders in relay across the prairies, plains, deserts, and mountains of the Western United States. For its 18 months of operation, it briefly reduced the time for mail to travel between the Atlantic and Pacific coasts to about ten days.