This doctoral thesis from Tubingen presents a new reflection on the topic of sin, in the form of a discussion of Julius Müller's Die christliche Lehre von der Sünde ('The Christian Doctrine of Sin' - first published 1839-44). In the judgement of Karl Barth, Müller's two-volume work is "the most important specialist literary work yet … that has treated this difficult material"; it is presented here for the first time in a comprehensive fashion and interpreted as a theory of freedom which moves towards an insight into the incomprehensibility of sin. Søren Kierkegaard "valued Müller's doctrine of sin most highly and benefited from it in his dispute with Hegel" (Emanuel Hirsch). An appendix documents the relevant diary passages on Julius Müller for the first time in German.