Standard components of importation (“classical”) biological control programs are the search for potentially effective natural enemies, the release and establishment of the enemies, and an evaluation of their ability to suppress target pests. Native pests pose somewhat different challenges and problems with respect to the discovery, handling, and evaluation of natural enemies than do exotic pests. With exotic pests, importation of new natural enemies is an accepted procedure; whereas for native pests, locally available enemies are given primary consideration. When dealing with native pests, a challenge for biological control researchers is to broaden the scope of surveys to include nontarget agroecosystems and, where appropriate, other regions or countries. This approach will require determining the complete geographic range of native pests. For both native and exotic pests, the effectiveness of natural enemies may be reduced if habitat resources are lacking or if other adverse environmental conditions exist. Conservation of natural enemies can be improved by developing experimental evaluation procedures to reveal factors that enhance and interfere with natural enemies. Where local natural enemies are shown to be ineffective against native pests, the collection and release of new enemies should be considered. This approach may involve introducing different geographic populations of existing natural enemy species, or the importation of new natural enemies that are affiliated with host and prey species that are closely related to the target pest. The latter procedure has been debated, both by biological control practitioners and those concerned about impacts on nontarget organisms. Thus, it presents a particularly interesting challenge. Many issues pertaining to natural enemy evaluation exist, both for native and exotic pests. These include correctly identifying pest and natural enemy species, understanding individual versus combined impacts of enemies, and assessing the impact of cryptic predators, parasitoids, and pathogens.