Mathilde Jacob (8 March 1873 – 14 April 1943) was a German typist and translator who during the First World War became politically involved, working with the anti-war Spartacus League and as a founder member of the German Communist Party. She came to politics through her work for Rosa Luxemburg, whose friend and close confidant she became. Although Mathilde Jacob continued to be politically engaged in the 1920s, her greater contribution to history comes from her having smuggled Luxemburg's letters and documents out of Luxemburg's prison cell during her friend's various incarcerations during the 1914–1918 war. She then preserved much of Luxemburg's written legacy after the latter's murder.