What explains the ebb and flow of religion? Some U.S. sociologists have argued that the demand for religion is relatively constant throughout history and across cultures and thus the fluctuations in religion are better accounted for by the supply-side factors such as the number and vigour of religious suppliers. Religious economies operate like commercial economies. Competition is said to be as beneficial for religion as it is for mundane products and results in greater religious vitality and overall levels of participation. This thesis is contrary to traditional secularisation theory, which maintained that religious pluralism undermined the plausibility and survival of all faiths. The religious market model and its supporting rational choice theory are examined in this essay. The bold claims of the model are not borne out by the empirical evidence. While the religious market model generates useful insights and data, its limits need to be observed.