This book deals with a novel aspect of a topical problem that is of widespread concern. Obesity and other eating disorders are significant human health problems that are proving highly resistant to prevention and cure. The recognition of important genotype/environment interaction in the causation of these problems and of the extensive genetic homology of higher animals justifies the importance of cross-species comparisons. The book covers observations made on animals in the wild as well as experimental data on laboratory animals and farm animals in order to lay out the basic genetic and environmental factors underlying the control of appetite (including diet selection) and body weight. Breakdown in these intricate mechanisms are then compared to examine the possible common candidate genes and their interaction with non-genetic factors, particularly the availability of diet choice and of levels of body activity. Animals have much to tell us about these mysteries and may significantly aid progress in dealing with what are still highly intractable and serious diseases of the modern world.