International Day of Peace, September 21

In 1981, the General Assembly declared that the opening day of its regular session in September "shall be officially dedicated and observed as the International Day of Peace and shall be devoted to commemorating and strengthening the ideals of peace both within and among all nations and peoples" (resolution 36/67). In 1998, the Assembly reaffirmed that the Day should continue to be observed on the opening day of its annual regular session (resolution 52/232 of 4 June).

On 7 September 2001, the Assembly decided that, beginning in 2002, the International Day of Peace shall be observed on 21 September each year, with this date to be brought to the attention of all people for the celebration and observance of peace (resolution 55/282). It declared that the Day shall henceforth be observed as a day of global ceasefire and non-violence, an invitation to all nations and people to honour a cessation of hostilities throughout the Day. It also invited Member States, United Nations bodies, regional and non-governmental organizations to commemorate the Day and to cooperate with the United Nations in establishing the global ceasefire.

Source: United Nations Website: Observations