Congress enacted the National Environmental Policy Act (NEPA) in 1969 and President Nixon signed it into law on January 1, 1970. Congress enacted NEPA to establish a national policy for the environment, provide for the establishment of the Council on Environmental Quality (CEQ), and for other purposes. NEPA was the first major environmental law in the United States and is often called the "Magna Carta" of Federal environmental laws. NEPA requires Federal agencies to assess the environmental effects of proposed major Federal actions prior to making decisions.

Section 101 of NEPA sets forth a national policy "to use all practicable means and measures, including financial and technical assistance, in a manner calculated to foster and promote the general welfare, to create and maintain conditions under which man and nature can exist in productive harmony, and fulfill the social, economic, and other requirements of present and future generations of Americans." 42 U.S.C. 4331(a). Section 102 of NEPA establishes procedural requirements, applying that national policy to proposals for major Federal actions significantly affecting the quality of the human environment by requiring Federal agencies to prepare a detailed statement on: (1) the environmental impact of the proposed action; (2) any adverse effects that cannot be avoided; (3) alternatives to the proposed action; (4) the relationship between local short-term uses of man’s environment and the maintenance and enhancement of long-term productivity; and (5) any irreversible and irretrievable commitments of resources that would be involved in the proposed action. 42 U.S.C. 4332(2)(C).

NEPA ensures agencies consider the significant environmental consequences of their proposed actions and inform the public about their decision making. Countries and non-governmental organizations all over the globe have created their own environmental impact assessment programs, modeled upon NEPA, making NEPA an international catalyst in the field of environmental protection.