Microbial plant pathogens causing qualitative and quantitative losses in all corps are present not only in the infected plants, but also in the environmental comprising of soil, water and air. The vectors present in the environment spread the microbial pathogens to short and/or long distances. Detection of microbial pathogens rapidly and reliably by employing suitable sensitive applicable for different ecosystems. The pathogens have to be identified precisely and differentiated and quantified to plan appropriate short-term and long-term strategies to contain the incidence and spread of diseases induced by them. This book aims to present all relevant and latest information on the detection techniques based on the biological, biochemical, immunological and nucleic acid characteristics of microbial pathogens presents in the host plants, as well as in the natural substrates that support the survival and perpetuation of the pathogens.