Otto Mainzer (26 November 1903 in Frankfurt am Main – 28 June 1995 in New York City) was a German-American writer.
There he made the acquaintance of André Gide, Heinrich Mann, Arnold Zweig and Erwin Piscator, who supported him financially.
At the time of his Paris exile, Mainzer became acquainted with the writings of psychoanalyst Wilhelm Reich.
Under the influence of Reich's ideas about sex-economy, Mainzer produced some major works on sexual coercion.
There he met his girlfriend Ilse Wunsch and lived for 25 years, "unmarried, in two different apartments, but in an intimate love relationship" until they married.