Abstract: Chevron U.S.A. v. Natural Resources Defense Council, Inc. settled the now familiar principle of federal administrative law that a reviewing court must accept an agency's “reasonable” interpretation of a gap or ambiguity in a statute the agency is charged with administering. Less familiar is Bowles v. Seminole Rock & Sand Co., in which the Supreme Court explained that “the ultimate criterion” for judicial construction of an ambiguous regulation “is the administrative interpretation, which becomes of controlling weight unless it is plainly erroneous or inconsistent with the regulation.” Under that principle, a reviewing court must accept a “plausible construction of the . . . regulation,” even if it is not “the best or most natural one by grammatical or other standards.” The Chevron and Seminole Rock principles are superficially similar, but they presents vastly different structure incentives in the administrative state. Chevron affords an administrative agency deference to its interpretation of a statute enacted by Congress; hence, ambiguity in such a statute gives discretion to to Congress’s constitutional rival, the Executive Branch. In contrast, if Seminole Rock tells us that an agency's rules mean whatever it says they mean (unless the reading is plainly erroneous), the agency effectively secures the power of self-interpretation. This authority permits an agency to fill in regulatory gaps or ambiguities of its own making and relieves the agency of the cost of imprecision that it has produced. This state of affairs makes it that much less likely that an agency will give clear notice of its policies either to those who participate in the rulemaking process prescribed by the Administrative Procedure Act (APA) or to the regulated public. Seminole Rock deference also contradicts a major premise of our constitutional scheme and of contemporary separation of powers case law — that a fusion of lawmaking and law-exposition is especially dangerous to our liberties. From that starting point, this Article argues that the Court should replace Seminole Rock with a standard that imposes an independent judicial check on the agency's determination of regulatory meaning. In particular, it argues that courts should evaluate agency interpretations of regulations under the standard of judicial review prescribed by Skidmore v. Swift & Co. Under Skidmore, a court gives an agency interpretation the weight it deserves in light of the “thoroughness evident in the [agency's] consideration, the validity of its reasoning, its consistency with earlier and later pronouncements, and all those factors which give it the power to persuade, if lacking power to control.” That approach would restore an independent judicial check on the agency's interpretation of its own regulations while also recognizing that agency experience and expertise may be valuable in the interpretive process and that courts should be open to persuasion when an agency advances a well-reasoned interpretation of its rules.