Gratitude is a pivotal concept in the psychology of religion because it is one of the most frequently experienced emotions toward God. The authors developed a trait measure of Gratitude to God (GTG-T) and investigated the association between Gratitude to God and psychological and spiritual well-being in four studies. Study 1 provided evidence for the validity of the GTG-T as Gratitude to God was associated with overall well-being and predicted increases in spiritual well-being over time. Study 2 used a prospective design to show that Gratitude to God predicted increases in general gratitude. In a third study, results showed that Gratitude to God predicted increased grateful emotion and increased confidence in the existence of God over time. In Studies 2 and 3, mediation analyses supported the model that Gratitude to God enhances well-being by promoting generalized gratitude. Study 4 provided further valid evidence for the GTG-T and also showed that gratitude to God is much more strongly related to one’s heartfelt conception of God as loving than to their doctrinal conception of a loving God. Gratitude to God deserves additional scientific scrutiny in the psychology of religion and spirituality than it has received to date.