The processes of natural biological control maintain the so-called balance of nature. Left unchecked, any species has the reproductive capacity to cover much of the earth, but all species are subject to checks on population numbers. The manipulation of grazing animals for the purpose of attaining certain types of vegetation or densities of interacting species is a form of biological control. However, the professional field of biological control concentrates on the use of parasites, predators, and pathogens to reduce population densities of unwanted organisms to levels below economic significance. Biological control is defined as the planned use of living organisms to reduce the vigor, reproductive capacity, density, or effects of undesirable plants (Quimby et al 1991). Activities within this definition are foreign exploration, introduction, and testing of possible control organisms; augmentation of native controls; and developing resistant cultivars. When integrated with other techniques, it is commonly called “Integrated Pest Management (IPM).” Conditioning of livestock to avoid or select certain plants suggests possibilities for training animals to exert specific influence on vegetation. The future of rangeland grazing management includes IPM, better plants, trained animals, and biological control organisms.