Authority to regulate emissions from internal combustion engines in Canada rests with Environment Canada and Transport Canada. Under the Canadian Environmental Protection Act 1999 (CEPA 1999) , Environment Canada has the authority to regulate emissions from on-road engines, as well as from most categories of off-road engines. Authority to regulate emissions from aircraft, railway locomotives and commercial marine vessels remains with Transport Canada.
The general approach to setting vehicle emission standards in Canada has been to harmonize them with US EPA federal standards. In 1988, on-road vehicle emission standards were first aligned with the US federal standards. In February 2001, the Minister of the Environment in the Federal Agenda on Cleaner Vehicles, Engines and Fuels  set out a number of policy measures that continued the harmonization of on-road emission standards, as well as expanded this harmonization by developing emission standards for off-road engines and standards for fuels that are aligned with the federal US requirements.
An important aspect of the harmonization with US standards is the recognition of emission certificates issued by the US EPA. Under most Canadian regulations—including emission standards for light-duty vehicles, heavy-duty engines and off-road engines—there are two ways of demonstrating emission compliance:
- US EPA emission certificate—Every model of vehicle or engine that is certified by the US EPA and that is sold concurrently in Canada and the United States is required to meet the same emission standards in Canada as in the United States. Most vehicles and engines are sold in Canada under this concurrent sales principle. These vehicles and engines must be affixed with a US EPA emission label and do not require a Canadian emission approval or labeling.
- Environment Canada emission approval—Vehicles and engines that do not have a valid US EPA emission certificate must be emission approved by Environment Canada and affixed with a Canadian emission label.
Certain US emission standards are phased-in over a number of years, with the respective US EPA regulations specifying detailed implementation schedules. Under the concurrent sales approach, the interim phase-in schedules may not be specified in the Canadian regulations. The final phased-in standards apply to all vehicles and engines sold in Canada beginning with the model year that they apply to 100% of a class of vehicles or engines in the United States.
On-Road Engines and Vehicles
Canadian federal regulations establishing exhaust emission limits for on-road vehicles were first promulgated in 1971 under the Motor Vehicle Safety Act which was administered by Transport Canada.
On March 13, 2000, under the Canadian Environmental Protection Act 1999 (CEPA 1999) , legislative authority for controlling on-road vehicle emissions was transferred from Transport Canada to Environment Canada.
In June 2001, Environment Canada signed a Memorandum of Understanding (MOU) with the Canadian Vehicle Manufacturers Association, the Association of International Automobile Manufacturers of Canada, and the member companies of those associations. The MOU formalized an industry commitment to market the same low emission light-duty vehicles and light-duty trucks in Canada as in the US for model years 2001-2003.
On January 1, 2003, the On-Road Vehicle and Engine Emission Regulations (SOR/2003-2)  were promulgated under CEPA 1999. The Regulations aligned vehicle and engine certification requirements with those of the US EPA beginning January 1, 2004 and including the US Tier 2 program for new light-duty vehicles, light-duty trucks and medium-duty passenger vehicles, and Phase 1 and Phase 2 programs for new heavy-duty vehicles and engines.
The Regulations set out technical standards for vehicles and engines for exhaust, evaporative and crankcase emissions, on-board diagnostic systems and other specifications related to emission control systems. The intention of the Regulations was to ensure that vehicles and engines meeting more stringent exhaust emission standards will begin entering the Canadian market in the 2004 model year and will be phased-in over the 2004 to 2010 model year period. The phase-in schedules can be summarized as follows: Tier 2 standards for light-duty vehicles and light light-duty trucks (2004-2007); Tier 2 standards for heavy light-duty trucks and medium-duty passenger vehicles (2004-2009); Phase 1 (2005) and Phase 2 (2008-2009) standards for complete heavy-duty vehicles; and Phase 1 (2004-2006) and Phase 2 (2007-2010) standards for heavy-duty engines.
On July 16, 2015, amendments were adopted to the On-Road Vehicle and Engine Emission Regulations  that harmonize Canadian requirements with the US EPA Tier 3 emission regulations, starting with the 2017 model year.
The On-Road Vehicle and Engine Emission Regulations also specify emission standards for motorcycles, which are aligned with US EPA emission standards.
Vehicle Weight Classes. The regulations define the weight classes for vehicles and engines as outlined below:
|Class||GVWR, kg (lb)|
|Light-Duty Vehicle||≤3,856 (8,500)|
|Light-Duty Truck||≤3,856 (8,500)|
|- light light-duty truck||≤2,722 (6,000)|
|- heavy light-duty truck||>2,722 to 3,856 (6,000 to 8,500)|
|Medium-Duty Passenger Vehicle||3,856 to <4,536 (8,500 to 10,000)|
|Complete Heavy-Duty Vehicle (Otto cycle only)||3,856 to 6,350 (8,500 to 14,000)|
|Heavy-Duty Vehicle/Heavy-Duty Engine||>3,856 (8,500)|
|- light heavy-duty engine||<8,847 (19,500)|
|- medium heavy-duty engine||8,847 to 14,971 (19,500 to 33,000)|
|- heavy heavy-duty engine||>14,971 (33,000)|
Off-Road Engines and Vehicles
Emission regulations have been adopted for the following categories of off-road engines:
- Off-Road Compression-Ignition Engines, such as those used in construction and agricultural machinery,
- Off-Road Small Spark-Ignition Engines, and
- Marine Engines
The authority for regulating railway locomotive emissions lies with Transport Canada under the Railway Safety Act. Environment Canada monitored locomotive emissions through information provided under a MOU signed by Environment Canada, the Canadian Council of Ministers of the Environment and the Railway Association of Canada in 1995. The MOU set a cap on annual NOx emissions from railway locomotives operating in Canada of 115,000 tonnes per annum. Since this agreement expired in 2005, locomotive emissions remain unregulated.