This book may serve to present the modern view of the universe to a large number of readers whose over-full professional commit ments leave them no time for the study of larger monographs ... Such a book should not be too compendious. Accordingly, the author has been at pains to allow the leading ideas of the various domains of astronomical investigation to stand out plainly in their scientific and historical settings; the introductory chapters of the three parts of the book ... , in the framework of historical surveys, should assist the general review. With that in mind, the title was chosen following Alexander von Humboldt's well known book "Kosmos, Entwurf einer physischen Weltbeschreibung" (1827-1859). On the other hand, particular results - which admittedly first lend colour to the picture - are often simply stated without attempting any thorough justification. The reader seeking further information will find guidance in the Bibliography. This makes no pretentions to completeness or historical balance. References in the text or in captions for the figures, by quoting authors and years, make it possible for the reader to trace the relevant publications through the standard abstracting journals. I wish to thank my colleagues V. WEIDEMANN, E. RICHTER and B. BASCHEK for their critical reading of the book and for much helpful counsel, and H. HOLWEGER for his tireless collaboration with the proofs. Similarly, my thanks are due to Miss ANTJE WAGNER for the careful preparation of the typescript.