(Uploaded by Plazi for the IPBES Invasive Alien Species Assessment) Classical biological control, as shown by successful programmes against weeds and insects, offers considerable advantages over other control methods. It is reasonably permanent, has no harmful side effects, attack is limited to a very small group of related species, agents are self-perpetuating, often density dependent and self-disseminating. This chapter brings a different perspective to the subject of biological control of plant pathogens. Using the example of a major pathogen, Phytophthora cinnamomi, the chapter approaches the question of its control as if it were an introduced weed that was to be subjected to classical biological control. The chapter outlines the theory of classical biological control, provides examples of the wide range of types of organisms and habitats that have been involved in this method, and presents a case for the classical biological control of P. cinnamomi.