Are there trans-religious, trans-cultural constants in psychological aspects of religion across different religions and cultures? An excessively culturalistic approach may overlook this possibility, putting an emphasis on the uniqueness of the religious phenomenon studied as emerging from a complex of multiple contextual factors. This article reviews empirical studies in psychology of religion in the 1990s that mainly include participants from different Christian denominations, but also from other religions: Muslims, Jews and Hindus. It appeared, at first, that several cross-cultural/religious differences can be documented (especially between Catholics and Protestants), but the interpretation of these differences is not simple, as other factors may interfere. Secondly it turned out that an impressive series of psychological constants also exist across different denominations, religions, and cultures. These constants include personality correlates, gender and gender orientation, positive and negative values, cognitive and affective aspects, identity formation, social attitudes and consequences.