Chevron v. NRDC

The Supreme Court ultimately approved EPA’s definition. In the course of the opinion, the Court stated that when a court reviews an agency’s construction of the statute it administers, that court must first determine whether Congress “has spoken to the precise question at issue.”

• If so, the inquiry ends, because the courts and agencies must “give effect to the unambiguously expressed intent of Congress.”
• If the statute is silent or ambiguous regarding the specific point, the court decides whether the agency interpretation is “based on a permissible construction of the statute.”

When Congress explicitly left a gap in a program to fill, the agency’s regulations are given controlling weight unless arbitrary, capricious, or manifestly contrary to statute. When such a gap is implicitly left by Congress, the court is not to substitute its own construction of the statute as long as the agency’s interpretation is reasonable.