ISSN 1522-5668 Journal of Religion & Society The Kripke Center Volume 13 (2011) 1 Religious Fundamentalism and How it Relates to Personality, Irrational Thinking, and Defense Mechanisms Louis Ernesto Mora, Pilgrim Psychiatric Center Wilson McDermut, St. John’s University Abstract This study explored how religious fundamentalism related to irrational beliefs and primitive defense mechanisms. We also explored how the personality factors of openness to experience and neuroticism moderated these relations. Participants (N = 120) were recruited in an urban area from a Northeastern university, a psychotherapy center, and through Internet advertising. The results demonstrated that religious fundamentalism predicted irrationality after controlling for degree of neuroticism. The results suggest that the degree of religious belief may be an important aspect of assessment when commencing psychotherapy because it relates to irrationality, which is the basis for psychopathology according to Rational Emotive Behavior Therapy. Therefore, rigidly held religious beliefs may predict psychopathology. Introduction [1] Historians and religious scholars have told us much about the phenomenon of religious fundamentalism, but the question remains as to how psychology can increase our understanding of this phenomenon. Is religious fundamentalism cultural, a form of psychopathology, or dimension of normal personality? Are there personality dimensions related to fundamentalist thinking? What does psychology tell us and how can we improve our understanding of the phenomenon of religious fundamentalism? [2] Altemeyer and Hunsberger defined religious fundamentalism as “the belief that there is one set of religious teachings that clearly contains the fundamental, basic, intrinsic, essential,