“Enthusiasm” has been described as the intellectual opposite of the Enlightenment, its “anti-self”. It stood for a religion of the “heart” rather than the “head”, and was associated with the extreme, millenarian sects on the fringes of established Protestantism. The relationship between religious enthusiasm and enlightened philosophy, however, could be closer than is often thought. Here I focus on the example of the jurist and philosopher Christian Thomasius (1655–1728), who is considered to be one of the first and most influential representatives of the early Enlightenment in Protestant Germany. Usually, Thomasius is described as a sort of classical enlightened thinker who separated the question of religious truth from the pursuit of secular philosophy, and it is implied that the interpretation of Thomasius's religious beliefs contributes little, if anything, to the understanding of his philosophical views. His religious views, however, not only were regarded by contemporaries as an example of religious “enthusiasm”. These “enthusiastic” religious beliefs were also more important to his philosophy than is often argued. They were part of a programme for religious and intellectual renewal and reform which, Thomasius believed, would prepare the reform of Lutheran philosophy from the obsolete, “scholastic” intellectual traditions it had inherited from the papal church. This essay examines the often complex development of Thomasius's religious views in their historical context and their significance for his wider “enlightened” intellectual interests.