Juan Bautista Justo (June 28, 1865, in Buenos Aires – January 8, 1928, in Buenos Aires) was an Argentine physician, journalist, politician, and writer. After finishing medical school he joined the Civic Union of the Youth, later participating in the foundation of the Socialist Party in 1896, of which he was chief director until his death. He married Alicia Moreau de Justo, with whom he had three children.