The fifth volume of the edition of the collected works of Viktor Frankl presents for the first time a complete collection of Frankl's writings on the relationship between psychology, psychotherapy, and psychiatry on one hand, and religiosity on the other, from the years 1934 to 1988. With these works, Frankl early on embarked on a path that has only recently become the subject of broader scientific interest: namely, the exploration of religious and spiritual motivations in a clinical context. Furthermore, the present works also generally attempt to do justice to the phenomenon of religion and spirituality from a psychological perspective, without solely explaining them in an inner-psychological, thus reductionist manner, but rather taking them seriously as existential phenomena.