Deep ecology is a recent branch of ecological philosophy (ecosophy) that considers humankind as an integral part of its environment. It places more value on other species, ecosystems and processes in nature than is allowed by established environmental and green movements, and therefore leads to a new system of environmental ethics.

The core principle of deep ecology as originally developed is Næss's doctrine of biospheric egalitarianism — the claim that all living things have the same right to live and flourish — a principle which, after criticism, has been substantially qualified (see Næss 1989). Deep ecology describes itself as "deep" because it is concerned with fundamental philosophical questions about the role of human life as one part of the ecosphere, rather than with a narrow view of ecology as a branch of biological science, and aims to avoid merely utilitarian environmentalism.