The life and work of Johann Salomo Semler (1725-1791) mirror the problems of Protestant Enlightenment theology in the 18th century and the beginnings of a historical-critical form of theology. After a biographical account, the study concentrates subsequently on Semler's understanding of the Bible, his hermeneutics, his stand on christological and soteriological questions and his approach to the idea of perfectibility. The reasons for his influential decision to distinguish between Christian religion and scholarly theology are analysed.