Do changes in religiosity beget changes in personality, or do changes in personality precede changes in religiosity? Existing evidence supports longitudinal associations between personality and religiosity at the between-person level, such that individual differences in personality predict subsequent individual differences in change in religiosity. However, no research to date has examined whether within-person changes in personality lead to subsequent changes in religiosity. Using random intercept cross-lagged panel models (RI-CLPM), we investigated between- and within-person associations between the Big Five personality traits and three aspects of religiosity-belief in God, service attendance, and prayer-in a sample of over 12,000 Dutch individuals across 11 annual assessments. We found between-person associations between all Big Five traits and religiosity, yet within-person associations only between agreeableness as well as extraversion and belief in God. Specifically, individuals who increased in agreeableness or extraversion reported subsequent increases in their belief in God and, in addition, individuals who increased in their belief in God showed subsequent increases in agreeableness. We further identified significant moderating effects of gender, religious upbringing, and religious affiliation. Overall, the present findings suggest that the associations between personality traits and religiosity primarily occur at the between-person level. However, the evidence for intraindividual associations between agreeableness, extraversion, and religious belief highlights the importance of distinguishing between-person from within-person effects to broaden the understanding of the temporal dynamics between variables. (PsycInfo Database Record (c) 2023 APA, all rights reserved).