Pollution is the introduction of harmful contaminants, from substances like plastics and gases to energy such as noise and radiation, into the natural environment, predominantly due to human activities like industrialization, agriculture, and poor waste management. Historically unregulated through much of the 19th and early 20th centuries, environmental regulations began emerging in the latter half of the 20th century to control both concentrated "point sources" and diffuse "nonpoint sources."

The consequences are dire, contributing to approximately nine million deaths globally in 2019—roughly one in six deaths that year—with air pollution being the leading cause. A 2022 review further highlighted that human-caused chemical pollution has exceeded planetary boundaries, gravely threatening ecosystems worldwide. Pollution disproportionately impacts vulnerable communities, fueling the environmental justice movement, and is increasingly addressed by local and international policies through bodies like the UN Environmental Program as a critical part of achieving Sustainable Development Goals.