The Expo Line is the oldest line of the SkyTrain rapid transit system in the Metro Vancouver region of British Columbia, Canada. The line is owned and operated by BC Rapid Transit Company, a subsidiary of TransLink, and links the cities of Vancouver, Burnaby, New Westminster and Surrey.

The line was originally known only as "the SkyTrain" from its inception in 1985 until 2002, as it was the system's only line during this time. In 2002, after the opening of the system's second line, the Millennium Line, the original line was given the name "Expo Line". The new name was in recognition of Expo 86, the world's fair that Vancouver hosted in 1986, as the transit system had been built in large part as a showcase and an attraction for that fair.

The line is elevated from Stadium–Chinatown to New Westminster stations, except for short at-grade sections between Nanaimo and Joyce–Collingwood stations in East Vancouver, and around the SkyTrain yards at Edmonds station in Burnaby.

The line travels underground for a short stretch between New Westminster and Columbia stations. Just east of Columbia is a junction, one branch of which crosses the Fraser River, via the SkyBridge, and is elevated for the rest of its run through Surrey, with King George as its terminus station. The other branch continues through New Westminster, first through a tunnel and then elevated until it terminates at Production Way–University in Burnaby.

From just west of Nanaimo station all the way to New Westminster station, the Expo Line follows the BC Electric Railway's former Central Park Line, which carried interurbans between Vancouver and New Westminster from 1890 to the early 1950s.

What is now known as SkyTrain began as a demonstration project to showcase the newly developed linear induction motor propulsion technology to Vancouver and other prospective cities throughout the world. Although Toronto's Scarborough RT was completed before the Expo Line in 1985, the Intermediate Capacity Transit System (ICTS) demonstration was the first system to use SkyTrain technology. The ICTS demonstration was built using the Advanced Rapid Transit (ART) technology developed by the Urban Transportation Development Corporation (now part of Bombardier). Construction began on March 1, 1982, and was completed in early 1983. The demonstration project consisted of just one station and about one kilometre of guideway with no switches. This original station was not named during this time as it was the only station, but then in 1985 opened as Main Street station.

As it was a showcase station, Main Street had a different initial design from other stations on the Expo Line that came after it. For example, glass was featured in the station's design, but was missing from other original Expo Line stations except Stadium station (now Stadium–Chinatown), since it was tied to the Expo grounds. Having preceded other stations on the line by three years, Main Street–Science World was visibly older, and signs of rust and wear were showing before extensive renovations to the station were completed in 2014.

The guideway for the showcase line was a straight section east of the station running over Terminal Avenue. It ended across from where the former Brussels Chocolate factory once was, located on Terminal. There was no guideway west of the station as the track ended immediately at the west end of the platform, where the Vancity head office now stands.