Konrad von Megenberg, canon of Regensburg cathedral, wrote his »Book of Nature« between 1348 and 1350. It has come down to us in approx. 150 manuscripts, which makes it one of the most popular vernacular encyclopedias of the late Middle Ages. Konrad had a Latin version of Thomas of Cantimpré's »Liber de natura rerum« at his disposal, which he translated into German, adapting and extending it and also re-accentuating certain aspects of the work. This is the first critical edition of version A. It replaces Franz Pfeiffer's valuable 1861 edition. At a later stage, it will be supplemented by an introduction (Vol. I), a commentary (Vol. III) and a dictionary (Vol. IV).