Léonie La Fontaine is a Belgian pioneer feminist and pacifist. Active in the international feminism struggle, she was a member of the Belgian League for the Rights of Women, the National Belgian Women Council and the Belgian’s Women's International League for Peace and Freedom. Her brother was Henri La Fontaine, Belgian international lawyer and president of the International Peace Bureau who received the Nobel Prize for Peace in 1913, and was also an early advocate for women's rights and suffrage, founding in 1890 the Belgian League for the Rights of Women.
Very close to the Mundaneum project, initiated by Paul Otlet and his brother Henri La Fontaine and to the notion of documentation, she initiated the Office central de documentation féminine in 1909, and created in her own home a library for the Belgian League for the Rights of Women, to help women in their professional choices. Léonie La Fontaine died on 26 January 1949, the year when the law allowing women to vote came into effect.