The framework for judicial review of administrative interpretations of regulatory statutes set forth in the landmark Chevron U.S.A. v. Natural Resources Defense Council decision prescribes two analytic inquiries, and for good reason. The familiar two-step analysis is best understood as a framework for allocating interpretive authority in the administrative state; it separates questions of statutory implementation assigned to independent judicial judgment (Step One) from questions regarding which the courts role is limited to oversight of agency decisionmaking (Step Two).
The boundary between a reviewing court\u27s decision and oversight roles rests squarely on the question of statutory ambiguity. For while courts, using traditional tools of statutory interpretation, should decide directly whether statutory language permits or clearly excludes the possibility of a given agency interpretation, judges must withdraw to a supervisory role when agency choices fall within a zone of ambiguity left by congressional instructions. In that oversight role, courts may ask whether an agency employed appropriate processes or reasoning in making an interpretive choice. But if the choice was reached in a reasonable manner, judges must let the administrative interpretation stand. Thus defining the areas of ambiguity within which agencies possess primary interpretive authority constitutes a – if not the – central component of judges\u27 independent Step One task
