The International Day of Peace, established by a United Nations resolution in 1981 to coincide with the opening of the General Assembly, was first celebrated on the third Tuesday of September, 1982. Beginning 2002, the UN General Assembly set 21 September as the now permanent date for the International Day of Peace.
In establishing the International Day of Peace, the United Nations General Assembly decided that it would be appropriate "to devote a specific time to concentrate the efforts of the United Nations and its Member States, as well as of the whole of mankind, to promoting the ideals of peace and to giving positive evidence of their commitment to peace in all viable ways… (The International Day of Peace) should be devoted to commemorating and strengthening the ideals of peace both within and among all nations and peoples."
The Assembly’s resolution declared that the International Day of Peace "will serve as a reminder to all peoples that our Organization, with all its limitations, is a living instrument in the service of peace and should serve all of us here within the Organization as a constantly pealing bell reminding us that our permanent commitment, above all interests or differences of any kind, is to peace. May this Peace Day indeed be a day of peace."
(Quotes excerpted from the United Nations General Assembly Resolution UN/A/RES/36/67.)
(Quote from the UN resolution UN/A/RES/55/282 which amends the date of the International Day of Peace to 21 September):
“The Assembly, reaffirming the contribution that the observance and celebration of the International Day of Peace make in strengthening the ideals of peace and alleviating tensions and causes of conflict, (decided that) beginning with the fifty-seventh session, the Day should 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.”