The overall aim of this study was to develop the Islamic Well-Being Scale and examine the relationship between mental health and Islamic well-being. In this study, four sub-studies were performed to create the one-factor Islamic Well-Being Scale, perform a confirmatory factor analysis and validate the Islamic Well-Being Scale, differentially predict ill-being and well-being outcomes using the Islamic Well-Being Scale, and compare individuals with different Islamic belief levels using the Islamic Well-Being Scale. In total, 170 adults, 209 adults, 216 theological faculty students and 152 undergraduate educational faculty students participated in each sub-study. Several scales related to well-being and ill-being were used in this study. The Islamic Well-Being Scale was found to be valid and reliable. Islamic well-being was related to certain indicators of well-being and ill-being.