The National Environmental Policy Act (NEPA) is a cornerstone of environmental law that Congress enacted in 1970. NEPA celebrated its 50th anniversary earlier this month. NEPA has been the focus of extensive litigation and debate, impacting a wide range of projects from energy development and pipelines to highways and infrastructure improvements. In simplest terms, the statute requires federal agencies to conduct environmental reviews and obtain public input when undertaking a "major Federal action significantly affecting the quality of the human environment." 42 U.S.C. § 4332(2)(C). The courts have ruled that NEPA is a procedural statute that does not mandate specific results or a substantive outcome. Dept. of Transp. v. Pub. Citizen, 541 U.S. 752, 756-57 (2004). Rather, federal agencies must take a "hard look" at the environmental impacts of an agency's actions. Kleppe v. Sierra Club, 427 U.S. 390 (1976).