The Parti social démocratique du Québec (PSD ; English: Social Democratic Party of Quebec) was the Quebec wing of the Co-operative Commonwealth Federation. It was founded in 1939 as the Fédération du Commonwealth Coopératif and was led by Romuald-Joseph Lamoureux in the 1944 general election, by Thérèse Casgrain from 1951 to 1957 and by Michel Chartrand from 1957 to 1960. The name Parti social démocratique was adopted in 1955.