The report is an analysis of what ecology has to contribute to solving environmental problems. The first part discusses traditional ecological subjects such as population ecology, community ecology, etc.; and also discusses general aspects of environmental problem-solving, such as using projects as experiments, the problem of cumulative effects, and setting boundaries. The second part consists of 13 case studies of the application of ecological knowledge to environmental problem-solving. The cases include studies of a halibut fishery, population control of vampire bats, conservation of spotted owls, biological control of citrus pests (red scale), timber management, the effects of DDT, and of forest clearcutting.