This article outlines a new approach to the study of religious commitment. Starting with a variant on Schelling's classic model of mobility and segregation, we develop a multi-agent religion simulation (MARS) that incorporates insights from theories of religious choice, social influence, and preference formation. Compared to standard statistical methods, MARS does a better job of linking individual choices and collective outcomes. In particular, it demonstrates that stable regional patterns require a balanced combination of attachment to personal identity and adaptation to the social environment.Imagine the following magic trick: A statistician grabs a pair of urns, one with red balls and one with blue. He shakes the first urn and pours some of its red balls into the second urn, then shakes the second urn and pours some of its red-blue mixture back into the first. He continues this mixing process 10 or 20 times, and then finally tips over both urns so as to reveal their current contents. To everyone's surprise, the first urn contains only red balls and the second only blue. He then repeats his trick starting with a 60-40 red-blue mix of balls in the first urn and a 20-80 mix in the second, but no matter when we look, the color ratio in each urn never changes.Short of special props or slight of hand, one really would need magic to pull this off. Yet, a similar sort of magic characterizes religious regionalism in America and throughout the world. Visualize the American population as three hundred million "balls" -red if they regularly attend church and blue otherwise. The balls are distributed unevenly across regional "urns," with high proportions of religious "reds" in the Southeast and high proportions of nonreligious "blues" in the Pacific West. Each year, millions of these balls move from urn to urn. 1 And yet, year after year the regions maintain their distinctive character. Despite massive nonstop mixing, the South remains relatively religious while the West remains relatively irreligious.Researchers have studied mobility and regionalism for decades, using numerous data sets and increasingly sophisticated statistics. But their work does more to confirm the magic than to explain it. Thus Smith et al. (1998:504) conclude that "[s]omething about merely 'being' in the South . . . leads one to have a stronger religious commitment [and] detectable religious homogenization has still not occurred." Welch (1983:179) likewise observes that "[e]ven after statistical adjustment [for different demographics and different rates of mobility], the Western church membership trough is still quite marked. " And Finke (1989) shows that the American West has remained relatively "unchurched" for at least 150 years. 2 This article seeks to resolve the puzzle of religious regionalism, but it also seeks to do much more. We introduce a new multi-agent (MA) framework that helps scholars and students explore a wide range of generalizations about social dynamics and religious outcomes. Relative to regression and most other standard m...