Internal secularization is reconceptualized as religious authority's declining scope within religious organizations. It is analyzed as the outcome of intraorganizational conflics between elites of two parallel stuctures within denominations: religious authority and agencies. Using longitudinal data collected from 83 Protestant denominations, this article finds that, generally, religious authority has decreasing control over denominations' organizational resources. But internal secularization is neither complete nor irreversible. Drawing on organizational and social movement theory, this article connects variation in internal secularization primarily to variation in the extent to which both religious authority and agencies are centralized. Recently resurgent religious authority is discussed.