Crop diseases are known to be caused by various abiotic and biotic agents. Among the biotic agents, microbial plant pathogens — fungi, bacteria, phytoplasmas, viruses and viroids — accounts for significant quantitative and qualitative losses in agricultural and horticultural crops. It is essential to have adequate knowledge of various aspects of these plant pathogens. Information on precise identification of microbial plant pathogens, process of disease development, epidemiology, assessment of losses due to diseases, principles of disease management, their applications for containing the diseases and the possible ways of integrating the practices is required to develop and enhance the effectiveness of disease management systems suitable for different ecosystems. Basic plant pathological methods provided in the appendix and glossary of plant pathological terms presented in this book will help the students to have a clear understanding of the subject. Graduating students, researchers and teachers desirous of updating the information on different aspects of microbial plant pathogens and the diseases caused by them, will find this book to be useful.