Editors' Summary: Although NEPA requires the preparation of an EIS for every major federal action significantly affecting the environment, federal agencies often decide in particular cases that compliance with NEPA is satisfied by preparation of EAs. The decision not to prepare an EIS is usually based on a finding of no significant impact. When an agency's threshold NEPA decision is challenged in court, what is the appropriate standard of review? The federal courts of appeals answer this question in at least two different ways: some circuits use the "arbitrary and capricious" standard, while others inquire into the "reasonableness" of the agency's decision. Several courts have expressed doubt that there is any genuine distinction between the rival standards,and the Supreme Court has so far declined to settle the issue. The author of this Article surveys the federal case law on this question, exploring the approach of each circuit and taking issue with those who maintain that the difference between the standards is illusory. The vital difference, the author argues, is that courts using the reasonableness standard are more likely to substitute their own judgment for that of the agency, while courts adopting the arbitrary and capricious standard tend not to second-guess an agency's decision. Because he sees an important difference between these two approaches, the author urges the Supreme Court to grant certiorari to resolve the circuit split.