This article deals with the contributions to the psychology of religion made by Dr. Marianne Beth (1890-1984), an almost totally forgotten pioneer of the psychology of religion. The article especially contextualizes her initiative to turn “unbelief” into a topic for research in psychology of religion, and describes the tragic end the Nazi reign made to her development and career. Born as the daughter of a prominent Austrian Jewish lawyer living in Vienna, Marianne von Weisl received excellent intellectual training. Initially, her wish to become active in the same field as her father was frustrated by the injunction against women studying law. When this injunction was lifted, she went for a second doctorate in law, her first doctorate having been in the humanities. Marianne Beth became very active in public life (serving on the boards of many organizations, including international ones); she travelled and gave lectures and developed a large radius as a prolific author in newspapers and periodicals. Although clearly committed women's rights, she did not belong to any feminist movement. Her interest in psychology was certainly stimulated by her husband Karl Beth (1872-1959), a professor of systematic theology, who developed an increasing interest in both history and the psychology of religion. In fact, psychology of religion seems to have become the field in which the couple collaborated intellectually most. They were both involved in the founding of a “research institute” for the psychology of religion, of an international society for the psychology of religion, and of a journal for the psychology of religion. All these activities took place from the apartment of the Beths in Vienna, where the preparations for the First International Congress for the Psychology of Religion also occurred. That congress had as its theme; “the psychic causes of unbelief”. Even earlier than her husband, Marianne Beth had published on the topic of unbelief. Her interest may have been triggered by a call for papers by the internationally renowned KantSociety. The Society issued a prize for a treatise on “the psychology of belief” in 1928, which Marianne Beth then won. It is also possible, however, that the call for papers had been triggered after her initial publications on the subject. Her paper was published in the well-known journal Kant-Studien. There was a plan to publish the contributions to the 1931 congress in Vienna in book form in a series of three volumes, but only one was published, probably due to financial problems. The rest of the papers presented were published in the Zeitschrift für Religionspsychologie, edited by the Beths. (Marianne Beth's paper was also published in this journal.) As her publications since then show, she grew increasingly interested in empirical topics and approaches, and was broadly read in contemporary psychology. She authored numerous contributions to the Zeitschrift für Religionspsychologie. However, when Nazi-Germany annexed Austria in 1938, she left the country for the United States, taking both her children with her. Shortly afterwards, Karl Beth was also obliged to follow his family into exile. In the US, neither had any opportunity to pursue their interests in the psychology of religion; Marianne taught sociology briefly and German; Karl taught “comparative theology”. Nevertheless, Marianne Beth's impulse to turn “unbelief” into a research topic in the psychology of religion did have some lasting influence: the work of better-known psychologists of religion such as Rümke, Pruyser and Vergote are indebted to her, at least indirectly, as this article tries to show.