The Second Quebec Conference (codenamed "OCTAGON") was a high-level military conference held during World War II by the British and American governments. The conference was held in Quebec City, September 12 – September 16, 1944, and was the second conference to be held in Quebec, after "QUADRANT" in August 1943. The chief representatives were Winston Churchill, Franklin D. Roosevelt and the Combined Chiefs of Staff. Canada's Prime Minister William Lyon Mackenzie King was the host but did not attend the key meetings.

Second Quebec Conference Octagon
The Prime Minister's Reception hosted at the Château Frontenac
Host country	Canada
Date	September 12–16, 1944
Cities	Quebec City, Québec
Participants	United Kingdom  United States

Agreements were reached on the following topics: Allied occupation zones in defeated Germany, the Morgenthau Plan to demilitarize Germany, continued U.S. Lend-Lease aid to Britain, and the role of the Royal Navy in the war against Japan. Based on the Hyde Park Aide-Mémoire, they made plans to drop the atomic bomb on Japan.