Environment, an organism's surroundings. Environment includes other living things as well as such nonliving constituents as water, air, light, soil, and temperature. Ecology, a branch of biology, is largely concerned with the environment as it affects an organism or group of organisms. Sociology is concerned with human environments as related to social and cultural conditions. An important phase of psychology deals with the roles of environment and heredity in shaping a person's personality.

The quality of the environment in which humans and other organisms must live has become a vital issue since the middle of the 20th century. Modern technology and an ever-increasing human population have brought about pollution to such an extent that many scientists believe the continued existence of humans and other forms of life on earth is seriously threatened. Noise, pesticides, automobile exhaust fumes, smoke, industrial wastes, and sewage and other refuse—these are but a few of the pollutants that are causing environmental problems.