King's Highway 2, commonly referred to as Highway 2, is the lowest-numbered provincially maintained highway in the Canadian province of Ontario, and was originally part of a series of identically numbered highways which started in Windsor, stretched through Quebec and New Brunswick, and ended in Halifax, Nova Scotia. Prior to the 1990s, Highway 2 travelled through many of the major cities in Southern Ontario, including Windsor, Chatham, London, Brantford, Hamilton, Burlington, Mississauga, Toronto, Oshawa, Belleville, Kingston and Cornwall, and many other smaller towns and communities.

The Provincial Highway Network consists of all the roads in Ontario maintained by the Ministry of Transportation of Ontario (MTO), including those designated as part of the King's Highway, secondary highways, and tertiary roads. Components of the system—comprising 16,900 kilometres (10,500 mi) of roads and 2,880 bridges —range in scale from Highway 401, the busiest highway in North America, to unpaved forestry and mining access roads. The longest highway is nearly 2,000 kilometres (1,200 mi) long, while the shortest is less than a kilometre. Some roads are unsigned highways, lacking signage to indicate their maintenance by the MTO; these may be remnants of highways that are still under provincial control whose designations were decommissioned, roadway segments left over from realignment projects, or proposed highway corridors.