Johann Joachim Spalding (1714-1804) was the eighteenth century's most important Protestant theologian. Dedicated to the practice and theory of Christian religion, his lifework singled him out as a modern pioneer. In the broad and diverse exchanges maintained by Spalding, the Enlightenment's discourse culture and life-world were documented with an exemplary immediacy. The letters represent a captivating insight into his correspondence, which often led the way forward in the big theological, literary and philosophical debates of the time.