Dietrich von Freiberg, 1240/50 to around 1320, was one of the most original philosophers, theologians, and natural scientists of the earlier period. Following Albert the Great and Meister Eckhart, he was the only German to achieve the high office of Magister in Paris. Through thorough argumentation, he was the first to establish the theory of the rainbow, which is now considered correct. His personal connection to Meister Eckhart is documented, as is his influence on Eckhart's thinking. His writings provide a historically reliable access to Eckhart's work. Kurt Flasch, who initiated and directed the four-volume edition of Dietrich's writings from 1977 to 1985, first introduces Dietrich's intellectual world and then provides a philosophical-historical analysis of all of Dietrich's writings, tract by tract. This is the first comprehensive presentation of this thinker in a hundred years, based on reliable foundations for the first time.