December 1 - Netherlands New Guinea raises the new Morning Star flag and changes its name to West Papua.
December 2 - Cold War: In a nationally broadcast speech, Cuban leader Fidel Castro announces he is a Marxist-Leninist, and that Cuba will adopt socialism.
December 5 - U.S. President John F. Kennedy gives support to the Volta Dam project in Ghana.
- Tanganyika gains independence and declares itself a republic, with Julius Nyerere as its first President.
- The Australian government of Robert Menzies is re-elected for a sixth term.
December 10 - The Soviet Union severs diplomatic relations with Albania.
- The American involvement in the Vietnam War officially begins, as the first American helicopters arrive in Saigon along with 400 U.S. personnel.
- Adolf Eichmann is pronounced guilty of crimes against humanity by a panel of 3 Israeli judges.
December 14 - Walt Disney's first live-action Technicolor musical, Babes in Toyland, a remake of the famous Victor Herbert operetta, is released, but flops at the box office.
December 15 - An Israeli war crimes tribunal sentences Adolf Eichmann to die for his part in The Holocaust.
December 17 - A circus tent fire in Niterói, Brazil kills 323.
December 18 - India opens hostilities in its annexation of Portuguese India, the colonies of Goa, Damao and Diu.
- Portuguese surrender Goa to India after 400 years of Portuguese rule.
- Indonesian president Sukarno announces that he will take West Irian by force if necessary.
December 21 - In Congo, Katangan prime minister Moise Tshombe recognizes the Congolese constitution.
December 23 - Luxembourg's national holiday, the Grand Duke's Official Birthday, is set on June 23 by Grand Ducal decree.
December 30 - Congolese troops capture Albert Kalonji of South Kasai (who soon escapes).
December 31 - Ireland's first national television station, Telefís Éireann (later RTÉ), begins broadcasting. (source: Wikipedia)