Abstract: In National Cable & Telecommunications Ass'n v. Brand X Internet Services, the Supreme Court explained that, within the domain of unclear agency-administered statutes, a federal court is subordinate to an administering agency. When an administering agency speaks authoritatively, federal court practice reflects this. When an agency speaks only informally, however, federal court practice does not. Specifically, when construing an agency-administered statute absent an authoritative agency interpretation, a federal court errs, given its subordinate status, when it exercises independent judgment concerning what interpretation is best. Instead, that subordinate status requires a court to predict what authoritative interpretation the administering agency would adopt--just as a federal court would predict how a state's highest court would answer some unsettled question of state law. Adhering to this predictive approach requires in turn that a court assign significant--in most cases dispositive--evidentiary weight to agency interpretations contained within certain legal nonbinding instruments, in particular legal briefs. This is because the non-authoritative interpretations contained in such instruments will most often constitute the best available evidence concerning what an administering agency would say if it were to speak authoritatively. This conclusion is surprising given the central holding of United States v. Mead Corp. that interpretations contained in nonbinding instruments are not entitlted to controlling deference under Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc. What this article will suggest is that the central holding of Mead ought to be mostly moot since, even where controlling deference is not owed de jure, it is most often owed de facto.