Abstract Religion plays a vital role in the lives of individuals around the world. Most research within the psychology of religion literature has focused on the particular features that distinguish given faiths. However, there is a need to conduct cross-cultural research on religiosity on the basis of more adequate measures applicable across religions. This article innovatively proposes a Multi-Religion Identity Measure (MRIM), aiming to facilitate cross-cultural research within the psychology of religion. Drawing on social developmental theory, the MRIM conceptualizes religious identity as attained within three main domains: Religious Affirmation and Belonging, Religious Identity Achievement, and Religious Faith and Practices. The measure was administered to 457 high school students (of a mean age of 17.7 years) and 397 college students (of a mean age of 24.57 years) from Muslim backgrounds and diverse Christian denominations in Israel. The participants also answered questions on other measures, including religiosity and well-being. The results demonstrated a unified structure of the MRIM with adequate reliability and validity. The study concludes that the MRIM can be employed to examine religious identity and its correlates within different faiths. Keywords: adolescentsChristianmeasureMuslimreligious identityyoung adults Notes aItem reversed. ∗p < .001. ∗p < .001. ∗p < .001.