Book excerpt: The use of biocontrol agents and beneficial organisms for management of plant and pest diseases appears as an environment-friendly and economic procedure. However, this option is not always available, depending on the lack of knowledge on the mechanisms of natural regulation, locally effective. In this view, this eBook considers studies and experimental works illustrating a range of problems and solutions based on microbial resources, suitable for management of biotic stress factors. These examples show how detailed data and knowledge on the organisms involved are of paramount importance to achieve a sustainable and durable management capability.