Saint Catherine Street (officially rue Sainte-Catherine) is the primary commercial artery of downtown Montreal. It crosses the central business district from west to east, beginning at the corner of Claremont Avenue and De Maisonneuve Boulevard in the city of Westmount, traversing the borough of Ville-Marie, and ending on Notre Dame Street East just east of Viau St in the borough of Mercier–Hochelaga-Maisonneuve.

Saint Catherine Street once boasted Montreal's four prominent department stores: Eaton's, Morgan's, Ogilvy's, and Simpson's. Today, only Ogilvy's remains. However, the street remains a shopping destination, with many major retailers having large stores along the street, including the Hudson's Bay Company, Les Ailes de la Mode, La Maison Simons, Archambault, La Senza, Future Shop, and Roots. Additionally, many of Montreal's most prominent shopping complexes, including the Faubourg Sainte-Catherine, the Centre Eaton, les Cours Mont-Royal (a high fashion shopping mall), the Complexe Desjardins, the Complexe Les Ailes, Place Dupuis, Plaza Alexis-Nihon, Westmount Square, and Place Montreal Trust all make their home along this street. It also runs past or through Dawson College, Concordia University, McGill University, and UQAM.

Strip clubs which famously made their home on Saint Catherine Street have now declined in numbers, though a few prominent clubs, such as the infamous Supersexe, do remain along the length of the street. Sex shops and pornographic movie theatres are also common. None of these establishments actually share a block with any of the churches that are on the street, but most blocks in the downtown segment have one or more of these establishments.

The street runs parallel to the largest segments of Montreal's famous underground city. The series of interconnected office tower basements and shopping complexes (mentioned above) that make up this main thoroughfare lie immediately north of the street.

The Green line of the Montreal Metro was built to serve Saint Catherine Street; however, to avoid disrupting traffic on the street, it was built one block to the north, under what would later become De Maisonneuve Boulevard.

Montreal's Place des Arts, the city's primary concert venue, is located on Saint Catherine Street between Jeanne Mance and Saint Urbain streets.

The street is also home to the Christ Church Cathedral, the only church in Canada that sits atop a shopping mall, les Promenades de la Cathedrale; another important church, Saint James United Church, has recently had its concealing façade of commercial buildings removed. Other churches on the street include Saint James the Evangelist Anglican Church.

The Gay Village extends along Saint Catherine St. in the east end of downtown, between Saint Hubert and Papineau. Beaudry metro station, on the Green Line, provides the most convenient access to the Village.

The Montreal Forum, previous home to the Montreal Canadiens, is also located on St. Catherine Street at Atwater. It has since been turned into a shopping and movie theatre complex. Due to the Forum's presence on this street, St. Catherine Street was used as the parade route whenever the Canadiens won the Stanley Cup in their history.

The segment in the district of Hochelaga-Maisonneuve is also an important commercial area in that neighbourhood.