The Denver & Rio Grande Western Railroad (reporting mark DRGW), often shortened to Rio Grande, D&RG or D&RGW, formerly the Denver & Rio Grande Railroad, was an American Class I railroad company. The railroad started as a 3 ft (914 mm) narrow-gauge line running south from Denver, Colorado, in 1870. It served mainly as a transcontinental bridge line between Denver, and Salt Lake City, Utah. The Rio Grande was also a major origin of coal and mineral traffic.

The Rio Grande was the epitome of mountain railroading, with a motto of Through the Rockies, not around them and later Main line through the Rockies, both referring to the Rocky Mountains.