'Eureka' was the inter-Allied conference at Tehran in Iran (28 November/1 December 1943).

The primary figures at the conference were Prime Minister Winston Churchill of the UK, President Franklin D. Roosevelt of the USA and Premier Iosif Stalin of the USSR, and the conference was the first wartime meeting between the three world powers at which Stalin was present. It succeeded the 'Sextant' conference in Cairo and preceded the 'Magneto' and 'Terminal' conferences at Yalta and Potsdam.

The conference was deemed necessary to reassess and if necessary redirect the course of the war after the termination of hostilities with Italy and given the potentially decisive nature of events on the Eastern Front and in the war against Japan. The discussion was centred primarily on the opening of a 'second front' in western Europe.

At the same time a separate protocol pledged the three countries to recognise Iran’s independence.

Most importantly, though, the conference planned the final strategy for the war against Germany and its allies. It was agreed that the Allies should provide support, in the form of equipment, supplies and commando operations, for the partisan movement in Yugoslavia. It was agreed that it would be most desirable if Turkey should come into war on the Allied side before the end of the year, and that if Turkey found itself at war the USSR would support it. It was agreed that 'Overlord' would be launched in May 1944, in conjunction with an operation against southern France. It was agreed that the USSR should enter the war against Japan after the conclusion of hostilities in Europe. It was agreed that the military staff of the three powers should from then on keep in close touch with each other.

At the insistence of Stalin, the borders of post-war Poland were determined as the line of the Oder and Neisse rivers and the Curzon Line.

In the purely military sphere, other decisions included the abandonment of 'Buccaneer', to increase pressure on the Germans in Italy as a means of preventing the despatch of reinforcements to the Eastern Front, and to time 'Overlord' to coincide with the Soviet summer offensive of 1944.

The wide-ranging political accords, revised and finalised at the 'Magneto' conference, also included the treatment of Germany and Austria, and the establishment of spheres of influence.