Available here for the first time in English, Reality and Its Order is a remarkable philosophical text by Werner Heisenberg, the father of quantum mechanics and one of the leading scientists of the 20^th century. Written during the wartime years and initially distributed only to his family and trusted friends, the essay describes Heisenberg's philosophical view of how we understand the natural world and our role within it. In this volume, the essay is introduced by the physicist Helmut Rechenberg and annotated by the science historian Ernst Peter Fischer. The content, particularly within its historical context, will be of great interest to many physicists, philosophers and historians of science.