The Parti social démocratique du Québec (PSD) was the Quebec wing of the Cooperative Commonwealth Federation. It was founded in 1939 as the Fédération du Commonwealth Coopératif and was led by Thérèse Casgrain from 1951 to 1957 and by Michel Chartrand from 1957 to 1960. The name Parti social démocratique was adopted in 1955. The party was refounded in 1963 as the Nouveau Parti démocratique du Québec.