Since 1967 when Guy Swanson's challenging book, Religion and Regime, was published there have been several reviews attacking it on fairly specific points, but none of these reviews seems really to examine his basic premises and means for testing those premises. While the present reviewer has neither the space nor in some instances the knowledge to deal with all aspects of this comprehensive book, she has examined in some detail Swanson's basic thesis and model in order to show where they need modification. With greater care and flexibility in categorizing individual political units and by modifying Swanson's idea of immanence, his model could indeed help explain more than the official position on religion in a given state during the Reformation period. It could also be used in explaining the spread of Protestantism, whether or not it was officially accepted, and it could even be applied to the spreading of medieval heresies.