To many proponents of the National Environmental Policy Act (NEPA), the Act will never fully realize its promise as long as it remains enforceable only as a procedural requirement. During the first decade of NEPA's existence, an open issue arguably existed as to whether NEPA imposed enforceable substantive requirements as well as procedural ones.

In 1980, however, the U.S. Supreme Court removed any doubt on the subject in its terse decision in Strycker's Bay Neighborhood Council v. Karlen, where it held that a court's only role is to insure that NEPA's procedural requirements have been followed and that the agency has considered the environmental consequences of its action. The Supreme Court later succinctly summarized its procedural view of NEPA in Robertson v. Methow Valley Citizens Council:

The sweeping policy goals announced in §101 of NEPA are thus realized through a set of "action-forcing" procedures that require that agencies take a "hard look" at environmental consequences.... Although these procedures are almost certain to affect the agency's substantive decision, it is now well settled that NEPA itself does not mandate particular results, but simply prescribes the necessary process.... Other statutes may impose substantive environmental obligations on federal agencies, but NEPA merely prohibits uninformed--rather than unwise--agency action.