Editors' Summary: In Chevron U.S.A., Inc. v. Natural Resources Defense Council, Inc., the Supreme Court resolved a long-running dispute over the definition of "source" in the Clean Air Act nonattainment area new source review program. The Court ruled that EPA acted within the discretion left if by Congress in changing to a definition making "source" synonomous with "plant," and castigated the D.C. Circuit for inserting its own policy preferences into an equation Congress intended the Agency to solve. The author reviews the analysis and reasoning of the Court and concludes that the decision will restrain judicial review of agency decisionmaking and statutory interpretation. The Court suggested specific criteria for limiting judicial review and issued a strong general demand for deference. The author argues that the decision, while encouraging expansion of the "bubble policy," will have a narrower impact on Clean Air Act interpretation than on judicial review, because the Court skimmed over several difficult Clean Air Act issues in order to make its message on judicial review as strong as possible.