The influence of religion on delinquency has been debated for more than 30 years, and yet, there remains a lack of consensus about the nature of this relationship. In an effort to bring some clarity to this area, this study assesses the religion-delinquency literature by using a methodological approach to reviewing a body of literature that is new to the social sciences—the systematic review (SR). This SR revealed that the literature is not disparate or contradictory, as previous studies have suggested. Religious measures are generally inversely related to deviance, and this is especially true among the most rigorous studies. As criminologists continue to examine the neglected topic of religion or what has been referred to as the forgotten factor, this article is a warning that measurement issues around a complex topic like religion, or even spirituality or forgiveness, is of paramount concern. The findings further indicate that future research on delinquency may gain explanatory power by incorporating religious variables in relevant theoretical models.