Martin Luther's Treatise on Liberty is a stroke of luck among the vast richness of the reformer's writings. Rarely again he achieved to present the situation of man before God and with his neighbours in such a concise way. Therefore this writing has been frequently used as an elementary introduction to the work of Luther. There is however need for a commentary to understand the basic concepts of Luther which indeed are a challenge for the modern mind. The commentary given here is readily understandable without a theological background. Therefore the book is suitable both for secondary school teaching and for private study.The text is based on the German-German edition of Luther's works and thus permits a fast reading as well as a study of the original text in Early New High German.