Agricultural and forest pests lead to many plant diseases resulting in poor yield and productivity. Traditionally, chemical pesticides have been used to control these pests. However, the adverse health impacts of chemical pesticides have triggered parallel research in safe biological options. Nevertheless, biocontrol has come a long way ever since the commercialisation of the first Bacillus thuringiensis based biopesticide (sporeine) in the 1940s, however, still there are research gaps. New knowledge and practical experiences have been added over the last few decades. This book reviews research on biological control agents, including bacterial, fungal and viral biopesticides along with their advanced formulation options.