The Overland Route was a train route operated jointly by the Union Pacific Railroad and the Central Pacific Railroad/Southern Pacific Railroad, between the eastern termini of Council Bluffs, Iowa, and Omaha, Nebraska, and the San Francisco Bay Area, over the grade of the first transcontinental railroad (also called the "Pacific Railroad") which opened on May 10, 1869. Passenger trains that operated over the line included the Overland Flyer, later renamed the Overland Limited, with its eastern terminal in Chicago.

The Overland Route remains a common name for the line from northern California to Chicago, now owned entirely by the Union Pacific. The route is now primarily used for freight, with a few portions used by Amtrak's California Zephyr passenger train.

The name harkens back to the Central Overland Route, a stagecoach line operated by the Overland Mail Company between Salt Lake City, Utah, and Virginia City, Nevada, from 1861 to 1866, when Wells Fargo & Company took over the stagecoach's operation. Wells Fargo ended this stagecoach service three years later.

While the Council Bluffs/Omaha to San Francisco "Pacific Railroad" grade was opened in 1869, the name “Overland” was not formally adopted for any daily extra-fare train over the route until almost two decades later. On November 13, 1887, the Union Pacific inaugurated service of its Overland Flyer between Omaha and Ogden, Utah, where passengers and through cars were transferred to the Southern Pacific, which had acquired the CPRR's operations on that line in 1885 under a 99-year lease. The UP changed its designation to the Overland Limited on November 17, 1895, and service continued as a daily train under that name in one form or another for almost seven decades. For the first dozen years that the SP met the UP's Overland trains, however, it dubbed its service the "Ogden Gateway Route"; its connecting westbound trains operated as the Pacific Express and eastbound trains as the Atlantic Express. The SP finally adopted the name the Overland Limited in 1899 for its portion of the run as well.

The original 1,911 miles (3,075 km) of the route from Omaha to San Francisco traversed some of the most desolate (as well some of the most picturesque) lands of the western two-thirds of the North American continent. While the trip originally took low-fare emigrant trains a full week (or more) to complete, by 1906 the electric lighted all-Pullman Overland Limited covered the route in just 56 hours.

E. H. Harriman bought the bankrupt Union Pacific in 1897; in 1901, he assumed control of the Central Pacific and Southern Pacific as well. The rebuilding of the Overland Route followed: hundreds of miles of double track, hundreds of miles of signals, and dozens of realignments to reduce grades, curvature, and perhaps distance. (The rebuilding actually started before the CP/SP acquisition—the map in the May 1969 issue of Trains shows the Howell-to-Bossler stretch realigned in 1899.)

By 1926, the UP route from Council Bluffs/Omaha to Ogden was continuous double track, except for the Aspen Tunnel (east of Evanston, Wyoming), which remained a bottleneck until 1949. The CP/SP portion of the route was also largely double-tracked during this period, with the completion of such projects as the 1909 Hood Realignment between Rocklin and Newcastle, double-tunneling along the Sierra Grade including at Cisco and the summit (Tunnel #41), and the 1924 agreement to share tracks across Nevada with the Western Pacific Railroad's Feather River Route.

Among the most important improvements to the original grade was the Lucin Cutoff, a new 102.9-mile (165.6 km) stretch from just west of Ogden to Lucin, a few miles east of the Nevada border. It included a 12-mile (19 km) trestle on wooden pilings across the Great Salt Lake. Opened in 1904, this line cut 43.8 miles (70.5 km) off the line, eliminated 3,919 degrees of curvature, and removed 1,515 feet (462 m) of climb from the route, thus decreasing the steepest SP grade east of Lucin from 90 feet per mile to 21.