Administrative law, the branch of law which regulates the actions of the executive, is one of the more complicated areas of law. While it is considered an area of law unto itself, administrative law is a major element of such diverse areas of law as environmental law, immigration law, government contracts, tax law, and international trade law. There are two basic branches of administrative law:

Substantive Administrative Law

Substantive administrative law includes the statutes that establish the various state and federal agencies, as well as the massive body of regulations and rules promulgated by the agencies. In the U.S., federal regulations can be found in the Code of Federal Regulations (CFR) and the Federal Register (FR).

One of the recurring issues in administrative law is the doctrine of separation of powers. In the performance of their duties, administrative agencies often exercise both quasi-legislative and quasi-judicial functions.

In the early days of administrative law, there was some resistance to the delegation of broad legislative power to administrative agencies. The Supreme Court generally required Congress to make the basic policy determinations, and allowed agencies to ascertain the existence of "facts," see e.g. Field v. Clark, 143 U.S. 649 (1892) (upholding the delegation of power to suspend a statute allowing free imports if the President determined that foreign duties were "unreasonable"), or to "fill in the details," as in United States v. Grimaud, 220 U.S. 506 (1911) (upholding a statute which gave the Secretary of Agriculture the authority to promulgate rules and regulations for the protection of the national forests).

Modern cases require an "intelligible principle" or "primary standard" to be established by Congress, leaving only the implementation of the principles and standards to the agencies. These "standards" may be exceedingly broad and nebulous, as in the seminal case of J.W. Hampton & Co. v. United States, 276 U.S. 394 (1928), which gave the President the power to impose tariffs to "equalise" differences in production costs. However, in cases in which the delegation may have wide-ranging repercussions, as with air quality standards. In Whitman v. American Trucking Associations, 531 U.S. 457 (2001), the Court held that
[Congress] must provide substantial guidance on setting air standards that affect the entire national economy. But even in sweeping regulatory schemes we have never demanded, as the Court of Appeals did here, that statutes provide a “determinate criterion” for saying “how much [of the regulated harm] is too much.” 175 F. 3d, at 1034. In Touby, for example, we did not require the statute to decree how “imminent” was too imminent, or how “necessary” was necessary enough, or even—most relevant here—how “hazardous” was too hazardous. 500 U. S., at 165–167. Similarly, the statute at issue in Lichter authorized agencies to recoup “excess profits” paid under wartime Government contracts, yet we did not insist that Congress specify how much profit was too much. 334 U. S., at 783–786. It is therefore not conclusive for delegation purposes that, as respondents argue, ozone and particulate matter are “nonthreshold” pollutants that inflict a continuum of adverse health effects at any airborne concentration greater than zero, and hence require the EPA to make judgments of degree. “[A] certain degree of discretion, and thus of lawmaking, inheres in most executive or judicial action.”

513 U.S., at 475.

Similarly, issues arise as to the delegation of adjudicative power to an administrative agency. The Supreme Court has generally allowed for broad adjudicative power on the part of administrative agencies, as long as the statute and regulation upon which the adjudication is based provides "fair notice" of its requirements and the adjudication concerns "public rights," i.e. claims between private parties and the government. However, litigation amongst private parties may be adjudicated by an agency if the private right is a "new" right created by statute and assigned by statute to an administrative agencie, or if a case involving private rights arises out of a federal statute and the statute would not operate properly if the agency could not adjudicate the case.

Procedural Administrative Law

While there is a vast and ever-changing body of substantive administrative law in the form of agency rules, regulations, policy statements, decisions, etc., the more important branch of administrative law is procedural. Procedural administrative law concerns (1) agency rulemaking and (2) agency adjudication.

Agency Rulemaking

When promulgating regulations, agencies must follow certain procedures, set forth in the Administrative Procedure Act (APA). Under the APA, "rulemaking" refers to the adoption of generally applicable regulations of prospective application. The APA distinguishes primarily between legislative rules, which are made pursuant to a delegation of rulemaking power from the legislature and are as binding as a statute if they fall within the scope of the delegated power, and nonlegislative rules, which do not have the binding effect of a statute. Nonlegislative rules include interpretive rules, which state the agency's interpretation of statutes or prior legislative rules and policy statements, which describe the manner in which the agency intends to exercise its discretion.

While the Constitution does not require any particular procedure to be followed for agency rulemaking, some statutes require "formal rulemaking", which includes a formal hearing on the record and adherence to adjudicatory procedures. Courts generally avoid requiring this sort of procedure, as it is cumbersome and inefficient. Agencies generally follow "informal rulemaking procedure" when promulgating regulations. APA § 553. Certain statutes also require "hybrid rulemaking," which combines elements of both informal and formal rulemaking.

Informal "Notice and Comment" Rulemaking

The first step in informal rulemaking is the publication of a Notice of Proposed Rulemaking in the Federal Register. The notice must include (1) the time, place, and nature of the public rulemaking proceedings, (2) the legal authority/statutory basis for the proposed rule, and (3) either the terms or substance of the proposed rule or a description of the issues involved in it. APA § 553(b).

The agency must also disclose the basic, critical data on which it relies in adopting the rule, including the scientific methodology, statistical data, etc. This allows interested members of the public a meaningful opportunity to examine, comment on, and criticise the proposed rule.

Under APA § 553(c), the agency must also give "interested persons an opportunity to participate in the rulemaking through submission of written data, views, or arguments with or without opportunity for oral presentation."

After hearing all the public comments, the agency may end up substantially revising the original rule. This does not necessarily require the agency to start over with a new Notice of Proposed Rulemaking, unless the final rule is not a "logical outgrowth" of the proposed rule. If the final rule is logically connected to the proposed rule, the public is considered to have had an adequate opportunity to make its views known. A final rule will fail the "logical outgrowth" test if the proposed rule did not even let interested parties know that an issue in which they were interested was up for discussion. National Black Media Coalition v. FCC, 791 F.2d 1016 (2d Cir. 1986).