This book attempts to outline population genetics and quantitative ge­ netics as they pertain to animal breeding and to discuss the theoretical aspects of this field of agricultural activity. Therefore, it brings into focus the basic principles of animal breeding, which are illustrated with per­ tinent examples; however, it is not intended to give recommendations for particular situations. Since the first edition, considerable development has occurred both in the basic and in the more applied fields. This has modified and in some cases even changed previously held conceptions, necessitating a thorough revision of the first edition. The extent of work in this sphere has reached dimensions which preclude exhaustive discussion of all its aspects in a volume of this size. Nevertheless it is hoped that this introductory text will stimulate the reader to explore the subject in greater depth and inspire study of the original literature. It is further hoped that my teaching experience has had some no­ ticeable impact on style and presentation. lowe much to constructive critical comments on the first edition. I am grateful to Dr. D. L. Frape for his help in changing my own translation into readable English. M. Asbeck and E. Fuchshuber have completed an admirable job in typing my handwritten script and A. Pickal accomplished the careful drawing of fresh illustrations.