It would have been very easy to expand on all the sections of the first edition but I decided to try to retain the relatively short, introductory nature of the book. Some new material has been added, particularly where it has been possible to update data, and there has been some change of emphasis in places, in order to reflect changing world conditions. The book retains its original purpose, however, of introducing systems thinking as applied to agriculture. I am grateful to Angela Hoxey for help in preparing this edition, especially in relation to the preparation of tables and figures. C. R. W. SPEDDING v Preface to the First Edition The agricultural systems of the world represent a very large subject. Their study involves a great deal of fairly detailed knowledge, as well as a grasp of the structures and functions of the systems themselves. This book has been written as an introduction to such a study and it concentrates on an overall view, rather than on the detail, partly because of the need to relate the latter to some larger picture in order to appreciate the relevance and significance of the detail. This problem-of seeing the relevance of component studies and the significance of physical, biological and economic detail, and indeed principles-is encountered by many agricultural students right at the beginning of their university careers.