Enacted after decades of devastating man-made environmental disasters, NEPA is one of the oldest piece of environmental legislation in the US. The act was signed into law by President Nixon and mandates that all federal agencies undergo a thorough process to assess a project’s potential impact on the environment.
If it's determined that a project will have a significant impact on the environment, agencies must submit a report known as an environmental impact statement (EIS), which details all anticipated effects on the environment. The agency is required to research and propose viable alternatives that would reduce the project’s impact. EISs are made available to the public and are evaluated by the Office of Federal Activities.
Many states now implement their own version of NEPA. The act has also served as a template for environmental legislation for dozens of governments and large organizations around the world.