Since commercialization of Collego™ and Devine™ in the early 1980s, there has been a small but consistent research effort in the area of bioherbicides. The bioherbicide approach has promised effective weed management in cropping systems where the classical approach (using exotic natural enemies) is largely unsuitable. The overriding principle of the bioherbicide approach has been that a host-specific, coevolved natural enemy can be used as a bioherbicide when applied in simple formulations at inundative levels; however, two decades of research has effectively disproven this principle. Although research has revealed weaknesses in the bioherbicide approach, it has also revealed potential in a number of areas. A number of niche situations will remain in which host-specific plant pathogens can be developed as bioherbicides, such as for parasitic weeds and narcotic plants, but more research should be conducted with virulent, broad host range organisms, and more effort should be devoted to developing techniques for the cultural and genetic enhancement of bioherbicidal organisms.