The International Day of Peace was first established in 1981 by resolution 36/67 of the United Nations General Assembly to coincide with its opening session every September. In 2001 resolution 55/282 was strengthened to fix the date annually on 21 September and for it to be a day of nonviolence and cease-fire. The resolution was adopted unanimously by the Member States of the General Assembly.
Resources page for 2010 International Day of Peace
UN Office for Disarmament Affairs
Disarmament, Peace and Security information resources