This comprehensive updated textbook makes an attempt to present the fundamental principles and concepts of plant pathology in a simple way for the beginners. It includes history of plant pathology, symptoms of plant diseases, host?parasite relationship and interaction, epidemiology and forecasting of plant diseases, effect of climatic conditions on plant diseases, physiologic specialization, defense mechanism, methods of studying plant diseases and principles of plant disease control. Though it is primarily written to cater to the requirements of undergraduate and postgraduate students of botany and plant pathology in faculties of science and agriculture, it will also be useful to the candidates preparing for different competitive examinations.