Longueuil is a city in the province of Quebec, Canada. It is the seat of the Montérégie administrative region and the central city of the urban agglomeration of Longueuil. It sits on the south shore of the Saint Lawrence River directly across from Montreal. The population as of the Canada 2021 Census totalled 254,483, making it Montreal's second largest suburb, the fifth most populous city in Quebec and twentieth largest in Canada.

The South Shore is the general term for the suburbs of Montreal, Quebec located on the southern shore of the Saint Lawrence River opposite the Island of Montreal. The South Shore is located within the Quebec administrative region of Montérégie.