The Administrative Procedure Act’s standard-of-review provision instructs reviewing courts to “decide all relevant questions of law, interpret constitutional and statutory provisions, and determine the meaning or applicability of the terms of an agency action,” and to set aside agency action “not in accordance with law.” How the APA’s statutory text might fit with the concept that courts should “defer” to agency legal interpretations is the subject of significant debate. Moreover, because deriving the meaning of the APA requires understanding the shifting law of the 1940s Supreme Court, the question is a conceptually and theoretically important one. This Essay seeks to understand the APA’s standard-of-review provision from the perspective of those who wrote it—by assessing the statute’s antecedents, text, structure, and legislative history, along with the other steps that Congress took during the 1940s to establish a standard-of-review in related areas.