The United Nations' International Day of Peace is celebrated each year on September 21st.
It was established in 1982 and celebrated on the first day of the opening of the United Nations General Assembly on September 21st, 1982. In 2002 the General Assembly declared September 21st as the permanent date for the International Day of Peace. The United Nations, as the initiators of this day, are dedicated to the promotion of world peace and an end to conflicts. They urge its member states to cooperate together in order to achieve this goal:

"Peace Day should be devoted to commemorating and strengthening the ideals of peace both within and among all nations and peoples…This day 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." (Discussion before the adoption of UN resolution that established International Peace Day).

Peacebuilding 101
(www.internationaldayofpeace.org)

Peacebuilding is different from "peacemaking" and "peacekeeping" in that it focuses on creating a long-term culture of peace, rather than solving existing conflicts or preventing old ones from re-occurring. Peacebuilding activities aim at building understanding and tolerance between individuals, communities and societies and establishing new structures of cooperation. Peacebuilding activities range in scale from personal acts of kindness toward others to global inter-governmental programs.

Definitions of Peacebuilding

Peacebuilding is the construction of new environments and new cultures which transform deficient structures and capabilities which unite the strengths of emerging innovations in all pathways of our local-global planetary life. Peacebuilding creates and maintains beneficial conditions for sustainable (life-enhancing) social, economic, political and spiritual development of all peoples.
(Adapted from speech given at UN by PTP and "An Agenda for Peace", a UN Report of the Secretary-General, 1992)

Unlike peace-making and peace-keeping, which are related to warfare and settlement of conflicts, "...the concept of peace-building (is) the construction of a new environment --- the transformation of deficient national structures and capabilities, and --- the strengthening of new democratic institutions."
(Excerpted from "An Agenda for Peace", a UN Report of the Secretary-General in January 1992, which globally and officially recognized the emerging field of peacebuilding.)