In Chevron U.S.A. v. NRDC, the U.S. Supreme Court upheld the Environmental Protection Agency’s (EPA) regulatory definition of “stationary source” as a reasonable construction of the Clean Air Act. Although important for administering the statute, the precedential reach of Chevron was far broader.

The Chevron doctrine, as it is commonly called, instructs federal courts to defer to an administrative agency’s reasonable interpretation of a statute that the agency is authorized to administer where the statutory language is silent or ambiguous. As a result, courts reviewing agency regulations will, at Chevron Step 1, examine whether Congress has spoken clearly on the question at issue. If the statutory language is ambiguous or silent on the question posed, at Chevron Step 2, courts will evaluate whether the agency’s interpretation is reasonable; not whether in the court’s view the agency’s interpretation is best.