United States Constitution
The Constitution of the United States is the "supreme law of the land;" it provides the basis for the United States government, and guarantees the freedom and rights of all United States citizens. No laws may contradict any of the Constitution's principles and no governmental authority in the United States is exempt from complying with it. The federal courts have the sole authority to interpret the Constitution and to evaluate the federal constitutionality of federal or state laws.

International Treaties
Treaties entered into by the United States are also considered the supreme law of the land pursuant to the United States Constitution, as are federal laws. In the case of a conflict between a treaty and a federal statute, the one that is later in time or more specific will typically control. Treaties to which the United States are a party may be found in the United States Treaties Service, the Statutes at Large, the Treaties and other International Acts Series issued by the State Department, as well as the United Nations Treaty Series. Treaties are often implemented by federal statutes.

Federal Statutes
Federal Statutes are published first in Slip Law, then in the Statutes at Large, and subsequently in the United States Code.

Agency Rules and Executive Orders
Federal administrative bodies issue rules and regulations of a quasi-legislative character; valid federal regulations have the force of law and preempt state laws and rules. Rules and regulations may be issued only under statutory authority granted by Congress. The President also has broad powers to issue executive orders. An executive order is a directive from the President to other officials in the executive branch. Proposed and final rules, executive orders, and other executive branch notices are published daily in the Federal Register. No person may be subject to any rule required to be published in the Federal Register and not so published. Every federal agency must publish: descriptions of its organizational structure; general statements of how the agency functions; its rules of procedures, available forms and descriptions of all papers, final reports or examinations; and, all substantive rules or statements of general applicability adopted by the agency. Rules may be challenged in federal court. The federal courts have sole authority to review agency rules and actions to ensure that they are legal under the substantive federal statute. Final administrative rules are published first in the Federal Register and then in the Code of Federal Regulation.

Judicial Opinions
The United States is a common law country. Every United States state has a legal system based on the common law, except Louisiana (which relies on the French civil code). Common law has no statutory basis; judges establish common law by applying previous decisions (precedents) to present cases. Although typically affected by statutory authority, broad areas of the law, most notably relating to property, contracts, and torts are traditionally part of the common law. These areas of the law are mostly within the jurisdiction of the states, and thus state courts are the primary source of common law. Federal common law is relatively narrow in scope, being limited primarily to clearly federal issues that have not been addressed by a statute.

Reported decisions of the United States Supreme Court and of most of the state appellate courts can be found in the official reporter of the respective courts. Those decided from at least 1887 to date can also be found in the National Reporter System, a system of unofficial reporters. Decisions of lower state courts are not published officially, but can usually be found in unofficial reports. When referring to a case, a citation typically includes the name of the case and the volume and pages of the reporter, as well as the date. For example, as follows: Kleppe v. New Mexico, 426 U.S. 529 (1976). Citations to federal courts of appeals are found in volumes abbreviated F., F.2d, or F.3d, and district courts are in volumes abbreviated F. Supp. The decisions of other specialized federal courts such as claims of bankruptcy decisions are also reported.

The system for citing state cases is similar. A correct citation would be: Wagen v. Ford Motor Co., 97 Wis. 2d 260, 294 N.W. 2d 437 (1980), meaning the case was decided in 1980, and is found on page 260 of volume 97 of the second series of Wisconsin State Reporters (the official reporter), as well as on page 437 of volume 294 of the second Northwestern set of the National Reporter System.

State Constitutions and Statutes
State constitutions are the supreme law within the state. State statutes must conform to the respective state's constitution. All state constitutions and legislation can be preempted by federal legislation or the federal Constitution. Municipal charters, ordinances, rules, and regulations apply only to local issues; they typically can be preempted by either state or federal law.

Citation Form
To ensure uniformity in citation styles for all law-related publications or writings, most citation to legal sources in the United States follows the Uniform System of Citation, also known as the Bluebook. The Bluebook is updated every few years by a consortium of law schools. Among other things, the Bluebook provides the abbreviations for all state and federal courts, statutory compilations, and administrative rules.