Victory in Japan Day, known as VJ Day, was celebrated on 15 August 1945, when Britain, the USA and other countries (known as the Allies), marked victory over Japan.
Since the fighting in Europe was already over, VJ Day was also the end of World War Two.
The war in Europe ended in May 1945 but many soldiers, sailors and airmen from the Allies were still fighting the Japanese in the Far East.
Japan surrendered in Autumn 1945.
The Allies had told Japan to surrender on 28 July 1945.
The deadline passed and the US then dropped two atomic bombs.
The Japanese city of Hiroshima was bombed on 6 August and Nagasaki on 9 August.
An estimated 71,000 soldiers from Britain and the Commonwealth died in the war against Japan, including more than 12,000 prisoners of war who died in Japanese captivity.
Japan treated prisoners of war very badly, including American and British soldiers who had surrendered.
Although VJ Day was celebrated on 15 August, the Japanese leaders did not officially surrender with a signed document until 2 September, and that date has also been known as VJ Day.