The Pioneer was an Amtrak long-distance passenger train that ran between Seattle and Chicago via Portland, Boise, Salt Lake City, and Denver. Operating from 1977 to 1997, the Pioneer was the last passenger rail route to serve Wyoming, Southern Idaho, or Eastern Oregon.

Rail advocates have been pushing for restoration of the Pioneer, though in 2021 Amtrak omitted the route from its 15-year expansion vision.

In the 1960s, prior to the creation of Amtrak, two Union Pacific Railroad streamliners provided service to Portland via Boise: the City of Portland (from Chicago) and the Portland Rose (from Kansas City). Amtrak did not retain either train in 1971—preferring the Empire Builder for Chicago–Pacific Northwest service—with the result that train travel between the Pacific Northwest and Denver required either going west to California or east to Chicago.

Amtrak sought to fill this gap in 1977 with the introduction of the Pioneer between Seattle and Salt Lake City. The all-coach train operated on a daily 24-hour schedule with connections available in Ogden, Utah with the Chicago–San Francisco San Francisco Zephyr. Meal service was provided in an on-board cafe, one of the then-new Amfleet dinettes. Coaches were reserved except between Portland and Seattle, where the Pioneer supplemented existing corridor service. In early 1977, Amtrak authorized approximately $500,000 to improve 13 stations along the route in Utah, Idaho, and Oregon. Work included installation of passenger shelters, platforms and rehabilitation of existing stations. Regular service began on June 7.

The Pioneer began exchanging a Seattle–Chicago through coach with the San Francisco Zephyr on April 26, 1981; this was supplemented by a through sleeping car on October 31, 1982. When the Denver and Rio Grande Western Railroad decided to join Amtrak in 1983, Amtrak renamed the San Francisco Zephyr to California Zephyr, shifted it south to the Moffat Tunnel Route, and changed its interchange point with the Pioneer from Ogden to Salt Lake City, the Pioneer's terminus.

On June 17, 1991, the Pioneer's terminus and California Zephyr interchange point was moved from Salt Lake City to Denver, its route was changed to use the Union Pacific's Overland Route in Wyoming (which had last seen service in 1983), and a bus was added between Salt Lake City and the Pioneer at Ogden. This change was made for two reasons:

The Pioneer was reduced to thrice-weekly on November 4, 1993.

In January 1997, Amtrak announced that the Pioneer would end May 10, 1997, when a Congressionally-funded mandate to keep it operating expired. States affected were given until March 15 to submit funding proposals to keep the train operating. While visiting Pendleton, Oregon on February 22, Amtrak President Thomas M. Downs said the Pioneer could be converted to a coach-only Chicago–Portland mail-and-express train operating on an all-Union Pacific routing through Iowa and Wyoming (but missing Ogden) if interested states could provide about $4.8 million to fund the existing operation through that October when the new train could start.