The National Environmental Policy Act (NEPA) of 1969 established an innovative process to protect the environment and the natural world. NEPA requires all federal agencies to consider the environmental effects of major actions they propose to undertake and to evaluate alternative actions with less adverse environmental impact. By introducing environmental considerations into the agency planning process and providing opportunities for public participation, NEPA seeks "to create and maintain conditions under which man and nature can exist in productive harmony."

A key step in the NEPA process is preparing an environmental impact statement (EIS). When proposing a major federal action that will significantly affect the quality of the human environment, the agency must develop a detailed statement on the environmental effects of its proposed action and any alternatives to the proposed action. As a procedural statute requiring federal agencies to take a hard look at environmental issues, NEPA does not alter the elements of the substantive statutes agencies administer. Agencies may undertake projects notwithstanding their environmental effects, as long as they articulate a reasoned explanation.