Ecology, the study of the ways in which living organisms influence and are influenced by the environment. Environment, in this sense, includes not only other living things but also such nonliving, natural constituents as chemical elements, moisture, soil, light, and temperature, and such man-made technological constituents as buildings, highways, machines, fertilizers, and medicines. Ecology is a branch of the science of biology. Specialists in this field are called ecologists.

The word ecology is sometimes used to describe the balance of nature, or the natural ways in which stability is maintained in the interactions of living and nonliving things. For example, pollution is said to disturb the ecology of a stream, meaning that it changes the ways in which fish, insects, algae, and water interact.

One of the main ways in which ecology is applied is through the conservation of natural resources.