21st September
Celebrated in all UN Member States
The International Day of Peace occurs annually on September 21. It is dedicated to peace, or specifically the absence of war, such as might be occasioned by a temporary ceasefire in a combat zone. It is a observed by many nations, political groups, military groups, and peoples.
To inaugurate the day, the "Peace Bell" is rung at UN Headquarters. The bell is cast from coins donated by children from all continents. It was given as a gift by the Diet of Japan, and is referred to as "a reminder of the human cost of war." The inscription on its side reads: "Long live absolute world peace.
Wikipedia