The Co-operative Commonwealth Federation – The Farmer-Labor Party of Ontario, more commonly known as the Ontario CCF, was a democratic socialist provincial political party in Ontario that existed from 1932 to 1961. It was the provincial wing of the federal Co-operative Commonwealth Federation (CCF). The party had no leader in the beginning, and was governed by a provincial council and executive. The party's first Member of the Legislative Assembly (MLA) was elected by voters in the 1934 Ontario general election. In the 1937 general election, no CCF members were elected to the Ontario Legislature. In 1942, the party elected Toronto lawyer Ted Jolliffe as its first leader. He led the party to within a few seats of forming the government in the 1943 general election; instead, it formed the Official Opposition. In that election, the first two women were elected to the Ontario Legislature as CCFers: Agnes Macphail and Rae Luckock. The 1945 election was a setback, as the party lost most of its seats in the Legislature, including Jolliffe's seat. The party again became the Official Opposition after the 1948 general election, and defeated the Conservative premier George Drew in his seat, when Bill Temple unexpectedly won in the High Park constituency. The middle and late 1940s were the peak years for the Ontario CCF. After that time, its electoral performances were dismal, as it was reduced to a rump of two seats in the 1951 election, three seats in the 1955 election, and five seats in the 1959 election. Jolliffe stepped down as leader in 1953, and was replaced by Donald C. MacDonald.

The Co-operative Commonwealth Federation was a federal democratic socialist and social-democratic political party in Canada. The CCF was founded in 1932 in Calgary, Alberta, by a number of socialist, agrarian, co-operative, and labour groups, and the League for Social Reconstruction. In 1944, the CCF formed one of the first social-democratic governments in North America when it was elected to form the provincial government in Saskatchewan.