Carnivores are often proposed as indicators of ecosystem function, or as keystone species in the top-down regulation of ecosystems. The strength of top-down processes varies widely among species and ecosystems, but is probably more prevalent than many ecologists have assumed. Wide-ranging carnivores may serve as 'bioassays' of emergent landscape characteristics such as connectivity and provide information on the optimal size and arrangement of reserves. Viability analysis of carnivore species may highlight potential conservation areas that are not targeted in other biodiversity assessments such as gap analysis. The restoration of mammalian carnivore species to portions of their former range, either by restoration of habitat through active reintroduction, presents challenges not encountered in most previous species restoration efforts. Besides the inevitable sociopolitical difficulties, large and medium-sized carnivores may be particularly sensitive to landscape configuration because of their low population densities and large area requirements.