The emerging science of conservation biology represents an intersection of elements of ecology, genetics, biogeography, and many traditional applied disciplines such as wildlife management and forestry. Its major concern is providing a valid scientific basis for actions that will slow or stop the accelerating loss of biological diversity worldwide. Ecology's major contributions to conservation biology so far include the equilibrium theory of island biogeography and the theoretical relationship between population size and persistence time. In the future ecologists can contribute their skills to conservation biology in numerous ways; I suggest three in particular. These are investigating the autecology and natural history of rare species, testing hypotheses concerning population viability with carefully designed laboratory and field experiments, and working to establish and implement a national policy for the protection of biological diversity on United States public lands.