The third Tuesday in September is the traditional start of the annual meetings of the United Nations General Assembly. In 1981, on this day, September 21, the General Assembly decided: "[This day] shall be officially proclaimed and observed as International Day of Peace and shall be devoted to commemorating and strengthening the ideals of peace both within and among all nations and peoples.”

The idea of such a "day of peace” is an old one. As far back as the 19th century, there were people in various European states who worked hard towards peaceful relations between nations and even called for them in public demonstrations.

In Germany, the World Peace Day is mostly marked on 1 September, because this day is also the anti-war day commemorating the beginning of the Second World War. But internationally, it is September 21 that is devoted to world peace.