This article sets forth a theory of competition between exclusive religions as an entry deterrence game, in which the incumbent may find it profitable not to accommodate but to deter the competitor's entry by precommitting to sufficient capacity expansion in the event of entry. If entry costs are high enough, deterrence is optimal and the incumbent remains a monopolist, although the entry threat distorts its effort upward. The model is then applied to the Catholic Church's reaction to the Protestant Reformation. It is argued that the model provides a better fit to the historical data of the Counter‐Reformation than the price‐cutting model proposed by economists Ekelund, Hébert and Tollison (, ).