The Union Pacific Railroad ( ), headquartered in Omaha, Nebraska, is the largest railroad network in the United States. James R. Young is president, CEO and Chairman.

UP's route map covers most of the central and western United States west of Chicago and New Orleans. As of 2005, UP operates on of track, of which it owns outright , both numbers representing the highest amount of any railroad currently operating in the United States. It has achieved this size thanks to purchasing a large number of other railroads, notably the Missouri Pacific, Chicago and North Western, Western Pacific, Missouri-Kansas-Texas, and the Rio Grande (including the Southern Pacific). Currently, Union Pacific owns 26% of Ferromex while Grupo Mexico owns the remaining 74%.

UP's chief railroad competitor is the BNSF Railway, which covers much of the same territory.