The Parti social démocratique du Québec (French pronunciation: [paʁti sɔsjal demɔkʁatik dy kebɛk], lit.
PSD) 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.
In November 1963, Quebec nationalists left the PSD to form the Parti socialiste du Québec; the latter was led by former PSD leader Michel Chartrand.
The NDPQ renamed itself the Parti de la Democratie Socialiste (Party of Socialist Democracy) following a 1991 split with the federal NDP over the question of Quebec independence.