This Article addresses the history of the Supreme Court’s interpretation of the Clean Air Act, which now goes back almost half a century. Many scholars have argued that the Court has shifted from an approach to statutory interpretation that relied heavily on purposivism—the custom of giving statutory goals weight in interpreting statutes—toward one that relies more heavily on textualism during this period. At the same time, proponents of dynamic statutory interpretation have argued that courts, in many cases, do not so much excavate a statute’s meaning as adapt a statute to contemporary circumstances.