Crop diseases are typically caused by a combination of abiotic and biotic factors. Among these biotic factors, microbial plant pathogens such as fungi, bacteria, phytoplasmas, viruses, and viroids can result in significant qualitative and quantitative losses for agricultural and horticultural crops. It is crucial to possess comprehensive knowledge about these plant pathogens and their various aspects. This includes information on the precise identification of microbial plant pathogens, the process of disease development, epidemiology, the assessment of losses due to diseases, disease management principles, and their applications for mitigating the spread of diseases. Developing and enhancing the effectiveness of disease management systems requires knowledge suitable for different ecosystems. The basic plant pathological methods provided in the appendix and the glossary of plant pathological terms presented in this book will help students gain a clear understanding of the subject. This book will be useful for graduating students, researchers, and teachers who wish to update their knowledge on the various aspects of microbial plant pathogens and the diseases they cause.