The First Transcontinental Railroad (known originally as the 'Pacific Railroad' and later as the 'Overland Route') was a 1,907-mile (3,069 km) contiguous railroad line constructed in the United States between 1863 and 1869 west of the Mississippi and Missouri Rivers to connect the Pacific coast at San Francisco Bay with the existing eastern U.S. rail network at Council Bluffs, Iowa.

Opened for through traffic on May 10, 1869 with the ceremonial driving of the 'Last Spike' at Promontory Summit, the road established a mechanized transcontinental transportation network that revolutionized the settlement and economy of the American West by bringing these western states and territories firmly and profitably into the Union and making goods and transportation much quicker, cheaper, and more flexible from coast to coast.