Abstract: Chevron v. NRDC, the foundation for much of contemporary administrative law, is now under siege. The central objection, connected with longstanding challenges to the legitimacy of the modern regulatory state, is that the decision amounts to an unwarranted transfer of interpretive authority from courts to the executive branch. Some people think that the transfer is a recipe for a form of authoritarianism – and inconsistent with the proposition that it is the province of the judiciary to say what the law is. To assess such objections, the starting point is simple: Whether courts should defer to agency interpretations of law depends largely on legislative instructions. Under the Constitution, Congress has broad power to require courts to defer to agency interpretations (in the face of ambiguity), or to forbid them from doing so. If congressional instructions are the touchstone, and if the Administrative Procedure Act is the guiding text, there is a plausible argument that Chevron was wrong when decided; but the issue is intriguingly cloudy if the APA’s text is taken in its context. In these circumstances, Chevron should not be overruled. Doing so would introduce a great deal of confusion and increase the role of political judgments within the courts of appeals. Nonetheless, Chevron’s critics have legitimate concerns. Those concerns should be taken into account (1) by insisting on a fully independent judicial role in deciding whether a statute is ambiguous at Step One; (2) by invalidating arbitrary or unreasonable agency interpretations at Step Two; and (3) by deploying canons of construction, including those that are designed to serve nondelegation functions and thus to cabin executive authority.