This book is a translation, by Mr. S. Dunlop, FRAS, of the second German edition of Veranderliche Sterne published by Johann Ambrosius Barth Ver­ lag, Leipzig, DDR, and Springer-Verlag, Berlin Heidelberg New York Tokyo. We have used the opportunity to make improvements and changes in a few places and to add details of new results and discoveries. The foreword to the second German edition remains no less valid for this one, including the changes. We would like to express our thanks to Mr. Dunlop for his expert and sympathetic translation and for the many improvements he suggested. December 1984 G. RICHTER and W. WENZEL Preface to the Second German Edition The suggestion that a second edition of this book should be prepared came equally from the readers, the publishers, and from the editors of the first edition. By a lucky coincidence the completion of the manuscript and the composition of these lines comes at the time of the 90th anniversary of the birth of Cuno Hoffmeister, the author of the first edition, and consequently this current work may be dedicated to his memory.