An environmental impact assessment (EIA) is a means for understanding the potential effects that a human action, especially a technological one, may have on the natural environment. It allows for the inclusion of environmental factors in making decisions by mandating a process for determining the range of environmental issues related to a particular action. The underlying assumption of an EIA is that all human activity has the potential to affect the environment to some degree, so that all major decisions should include environmental, as well as economic and political, factors. Understanding the potential environmental effects of an action helps policymakers choose which actions should proceed and which should not.

Many governments perform EIAs at the national, state, and local levels. Probably the best-known form of the EIA is the Environmental Impact Statement (EIS) of the United States government. The National Environmental Policy Act of...