In this study, I analyze the relationship between sexual permissiveness and affiliation with a fundamentalist religion and how this relationship has changed over time. I first consider previous research that reviews how religious affiliation, religiosity, and religious fundamentalism shapes sex attitudes and, therefore sexual permissiveness. I then review existing studies that discuss what factors influence permissiveness toward different sexual behaviors. Next, I discuss the mechanisms of religious institutions that influence sexual permissiveness. Prior literature motivates my research question as there is a lack of studies that explore sexual permissiveness across religious affiliations. This study fills a void in the existing literature by exploring the gap in sexual permissiveness between religious affiliations and how that gap has changed over time. After considering the current literature, I introduce a hypothesis exploring the relationship between sexual permissiveness and affiliation with fundamentalist religion. This study performs OLS regression using secondary data from the General Social Survey (GSS) that describes respondents' religiosity, religious affiliation, and attitudes towards sex. The study's findings show that affiliation with more fundamentalist groups is significantly correlated with more conservative sex attitudes reflecting lower levels of sexual permissiveness. The results also suggest that the gap in sexual permissiveness between those that affiliate with liberal, moderate, and fundamentalist religions has become larger over time.