Despite methodological advances in studying the relationship between religious attendance and volunteering, its dynamic nature still needs to be elucidated. We apply growth curve modeling to examine whether trajectories of religious attendance and volunteering are related to each other over a 15-year period in a nationally representative sample from the Americans’ Changing Lives data (1986-2002). Multivariate results showed that the rates of change in religious attendance and volunteering were positively related, and excluding religious volunteering did not alter the finding. It was also found that the initial level of religious attendance was positively associated with the rate of increase in volunteer hours over the period. Mediation analyses revealed that participation in voluntary associations explained the dynamic relationships between religious attendance and volunteering. These results provide evidence that involvement in organized religion and volunteering are dual activities that change together over the adult life course.