I offer these two cases ... CHEVRON U. S. A. INC. v. NATURAL RESOURCES DEFENSE COUNCIL When a court reviews an agency's construction of the statute which it administers, it is confronted with two questions. First, always, is the question whether Congress has directly spoken to the precise question at issue. If the intent of Congress is clear, that is the end of the matter; for the court, 843*843 as well as the agency, must give effect to the unambiguously expressed intent of Congress. If, however, the court determines Congress has not directly addressed the precise question at issue, the court does not simply impose its own construction on the statute, as would be necessary in the absence of an administrative interpretation. Rather, if the statute is silent or ambiguous with respect to the specific issue, the question for the court is whether the agency's answer is based on a permissible construction of the statute. "The power of an administrative agency to administer a congressionally created . . . program necessarily requires the formulation of policy and the making of rules to fill any gap left, implicitly or explicitly, by Congress." If Congress has explicitly left a gap for the agency to fill, there is an express delegation 844*844 of authority to the agency to elucidate a specific provision of the statute by regulation. Such legislative regulations are given controlling weight unless they are arbitrary, capricious, or manifestly contrary to the statute. Sometimes the legislative delegation to an agency on a particular question is implicit rather than explicit. In such a case, a court may not substitute its own construction of a statutory provision for a reasonable interpretation made by the administrator of an agency. Note the wording indicating the standard necessary for a nexus between the statute and regulation does not appear to be particularly high: ?Such legislative regulations are given controlling weight unless they are arbitrary, capricious, or manifestly contrary to the statute? CHRYSLER CORP. v. BROWN, SECRETARY OF DEFENSE, ET AL In order for a regulation to have the "force and effect of law," it must have certain substantive characteristics and be the product of certain procedural requisites. The central distinction among agency regulations found in the APA is that between "substantive rules" on the one hand and "interpretive rules, general statements of policy, or rules of agency organization, procedure, or practice" on the other. A "substantive 302*302 rule" is not defined in the APA, and other authoritative sources essentially offer definitions by negative inference. But in Morton v. Ruiz, 415 U. S. 199 (1974), we noted a characteristic inherent in the concept of a "substantive rule." We described a substantive rule?or a "legislative-type rule," id., at 236?as one "affecting individual rights and obligations." Id., at 232. This characteristic is an important touchstone for distinguishing those rules that may be "binding" or have the "force of law." Id., at 235, 236. That an agency regulation is "substantive," however, does not by itself give it the "force and effect of law." The legislative power of the United States is vested in the Congress, and the exercise of quasi-legislative authority by governmental departments and agencies must be rooted in a grant of such power by the Congress and subject to limitations which that body imposes. As this Court noted in Batterton v. Francis, 432 U. S. 416, 425 n. 9 (1977): "Legislative, or substantive, regulations are `issued by an agency pursuant to statutory authority and . . . implement 303*303 the statute, as, for example, the proxy rules issued by the Securities and Exchange Commission . . . . Such rules have the force and effect of law.