organization whose opposition to war dates from World War I, which makes it the oldest continuously active peace organization in the United States. It encompasses some 100 branches in the United States and has other branches in approximately 50 countries. Philadelphia is the site of the U.S. headquarters, and Geneva is the home of the international headquarters.

Officially, the WILPF came into being in 1919 at the end of World War I, but it evolved from the Women's Peace Party (Woman's Peace Party), a pacifist organization founded by Jane Addams (Addams, Jane) and others who attended the International Congress of Women at The Hague in April 1915. At the time, speaking out against the war was considered radical and unpatriotic, and some members of the Women's Peace Party paid a high price for their sentiments. The economist Emily Greene Balch (Balch, Emily Greene) lost her professorship at Wellesley College, and Addams was declared “the most dangerous woman in America.” Eventually, the pacifist work of Addams and Balch was recognized—both won Nobel Peace Prizes (in 1931 and 1946, respectively).

Throughout the 20th century, the WILPF persisted in its mission of opposing war and striving for political, economic, social, and psychological freedoms for all and remained firm in the belief that such freedoms are always severely compromised by the threat of war. Currently, the WILPF has identified as its main priorities disarmament, racial justice, and women's rights. The organization formed alliances with such other activist organizations as the Nuclear Weapons Freeze Campaign and the Women's Speaking Tour on Central America to increase support and publicity for its objectives.