Pacifism is closely linked to the history of the Mundaneum and the lives of its founders. The archives on the movement cover a period spanning the dawn of the pacifist movement in Belgium in the last quarter of the 19th century to the late 20th century.

Since 1993, the numerous documents on pacifism and internationalism contained in Otlet and La Fontaine’s archives have been supplemented by more recent collections, including:

• some of the personal papers belonging to Jean Van Lierde (1926-2006), an important figure in the War Registers’ International (WRI), and the fight for the right to conscientious objection in Belgium;
• the archives of the Maison de la Paix de Charleroi;
• the archives of the CNAPD or National Coordination for Peace and Democracy founded in 1970, which is best known for its work in the anti-nuclear-missile movement of the 1970s and 1980s;
• the archives of the CNCD or the National Centre for Cooperation and Development, which was founded in 1966 to unite associations active in supporting Third World countries and refugees — the CNCD is best known for the 11.11.11 operation it carries out every year;
• some of the archives of the Christian Movement for Peace, an ecumenical and anti-violence movement founded in Liège in the 1950s.