In September 1939 Heisenberg was conscripted for service at the Ministry of Ordnance in Berlin. He became a member of the so-called "Uranium Club" and participated in the preliminary preparation for the construction of a Uranium reactor. This secret work of Heisenberg's entailed, aside from fundamental theoretical investigations, also experiments at the University of Leipzig with his colleague Robert Döpel and his wife Klara, as well as the supervision of the experiments done at the "Kaiser Wilhelm-Institute for Physics" in Berlin Dahlem. In July 1942 Heisenberg was named chief director of the Berlin institute. His multi-faceted activity - pure theoretical Physics also was not neglected, as the seminal publications on the S-matrix theory of elementary particles in the years 1942 and 1944 show! - was interrupted for vacation periods in Urfeld on Lake Walchen where Heisenberg had acquired a summer house in the summer of 1939. There a part of a manuscript of 200 pages, philosophical in content, was created that relates very closely to the five lectures printed in this volume of his works.

The lecture in Budapest on the theory of color had been received favorably so that Heisenberg was prompted to think more about the questions of methodology in the natural sciences. Consequently, he not only gave another series of lectures such as in Leipzig and Zurich, but he also authored an in-depth manuscript in which he wrote down the sum total of his previous views and also enlarged on them to include new realms of the natural sciences and of the description of reality.

The manuscript, finished in the fall of 1942, is untitled. We have named it "Reality And Its Order" in accordance with a remark Heisenberg makes in the text. It consists of three parts, an introduction (I.), the main body (II.) and a summation (III.) It was not meant for publication, but typed copies of it were sent to reliable friends at Christmas 1942. (In the latter parts of part II. and in part III. there are political statements, which could have become dangerous for the author in the Germany of that time, especially given that he was working in a leading role on projects of wartime significance).

This text is based on the handwritten manuscript, which contains some corrections compared to the typed copy.

• From Werner Heisenberg, Collected Works. Section C: Philosophical and Popular Writings. Volume I. Physics and Cognition. 1927-1955