This book is about how plants get diseases, from the origins and evolution of parasites to how the great plant epidemics developed. The basic premise of the book is that the conditions favouring disease are inherent in agriculture and that diseases become destructive because of human activities. It also deals with how people have dealt with plant diseases in history. Included in the book are the natural histories of some of the most damaging plant diseases, worldwide, with discussions of why each became destructive. Diseases are grouped according to the most significant factors in the development of epidemics: in every case this is due to a human factor. Discussion of each model disease proceeds from observable facts to more complex concepts; thus, the reader with little knowledge of plant pathology should find the book easily understandable.