The Canadian province of Ontario has joined ICAP as its 29th member. John Gerretsen, Minister of the Environment, signed the ICAP declaration on 3 June 2009 .

In 2007, Ontario announced its Climate Change Action Plan for reducing greenhouse gases, of which cap and trade is an integral part. Ontario is a member of the Western Climate Initiative (WCI). For more information on Ontario efforts with regard to emissions trading, please visit Ontario's website.