This article is concerned with Bertha Pappenheim as the patient Anna O. For her life before and after her treatment, see Bertha Pappenheim.

Anna O. was the pseudonym of a patient of Josef Breuer, who published her case study in his book Studies on Hysteria, written in collaboration with Sigmund Freud. Her real name was Bertha Pappenheim (1859–1936), an Austrian-Jewish feminist and the founder of the Jüdischer Frauenbund (League of Jewish Women).