In plant diseases the biocontrol agents are usually bacterial or fungal strains isolated from the endosphere or rhizosphere. Viruses can also be used as biocontrol agents and there is a resurgent interest in the use of bacterial viruses for control of plant diseases. In the present book, efforts has been made to collect the information on various aspects of biocontrol of plant diseases, control of nematodes, leaf, fruits, corn and vegetable diseases.