From left to right, Stalin, Roosevelt, and Churchill

The Tehran Conference was the meeting of Joseph Stalin, Franklin D. Roosevelt and Winston Churchill between November 28 and December 1, 1943 that took place in Tehran, Iran. It was the first war conference among the three world powers in which Stalin was present. It succeeded the Cairo Conference and was followed by Yalta Conference and Potsdam Conference. The chief discussion was centered on the opening of a second front in Western Europe. At the same time a separate protocol pledged the three countries to recognize Iran's independence:

"The Three Governments realize that the war has caused special economic difficulties for Iran, and they are agreed that they will continue to make available to the Government of Iran such economic assistance as may be possible, having regard to the heavy demands made upon them by their world-wide military operations, and to the world-wide shortage of transport, raw materials, and supplies for civilian consumption." (Declaration of the Three Powers Regarding Iran, December 1, 1943)

Most importantly the conference was organized to plan the final strategy for the war against Nazi Germany and its allies.

Military conclusions of the Tehran Conference

1. An agreement was made stating that the partisans of Yugoslavia should be supported by supplies and equipment and also by commando operations.
2. It was agreed that it would be most desirable if Turkey should come into war on the side of the Allies before the end of the year.
3. If Turkey found herself at war the USSR was obligated to support her.
4. Took note on November 30 that Operation Overlord would be launched during May 1944, in conjunction with an operation against Southern France.
5. Russia should enter the war against Japan after the end of the war in Europe.
6. It was agreed that the military staff of the Three Powers should from then on keep in close touch with each other.

Quotation

"We the President of the United States, the Prime Minister of Great Britain, and the Premier of the Soviet Union, have met these four days past, in this, the Capital of our Ally, Iran, and have shaped and confirmed our common policy." (Declaration of the Three Powers, December 1, 1943)

Teheran 43 was a movie made about the event.