Administrative law is the body of law that governs the activities of administrative agencies of government. Government agency action can include rulemaking, adjudication, or the enforcement of a specific regulatory agenda. Administrative law is considered a branch of public law. As a body of law, administrative law deals with the decision-making of administrative units of government (for example, tribunals, boards or commissions) that are part of a national regulatory scheme in such areas as police law, international trade, manufacturing, the environment, taxation, broadcasting, immigration and transport. Administrative law expanded greatly during the twentieth century, as legislative bodies worldwide created more government agencies to regulate the social, economic and political spheres of human interaction.

In the United States, many government agencies are organized under the executive branch of government, although a few are part of the judicial or legislative branches. In the federal government, the executive branch, led by the president, controls the federal executive departments, which are led by secretaries who are members of the United States Cabinet. The many independent agencies of the United States government created by statutes enacted by Congress exist outside of the federal executive departments but are still part of the executive branch. Congress has also created some special judicial bodies known as Article I tribunals to handle some areas of administrative law. The actions of executive agencies and independent agencies are the main focus of American administrative law. In response to the rapid creation of new independent agencies in the early twentieth century (see discussion below), Congress enacted the Administrative Procedure Act (APA) in 1946. Many of the independent agencies operate as miniature versions of the tripartite federal government, with the authority to "legislate" (through rulemaking; see Federal Register and Code of Federal Regulations), "adjudicate" (through administrative hearings), and to "execute" administrative goals (through agency enforcement personnel). Because the United States Constitution sets no limits on this tripartite authority of administrative agencies, Congress enacted the APA to establish fair administrative law procedures to comply with the constitutional requirements of due process. Agency procedures are drawn from four sources of authority: the APA, organic statutes, agency rules, and informal agency practice. It is important to note, though, that agencies can only act within their congressionally delegated authority, and must comply with the requirements of the APA. The American Bar Association's official journal concerning administrative law is the Administrative Law Review, a quarterly publication that is managed and edited by students at the Washington College of Law.