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Primary documents such as statutes, regulations, rulings, court opinions; secondary resources such as dictionaries, directories, and law reviews; and tips on researching and writing about the law.

Introduction to the Law

This is a guide to sources of primary documents related to the law, such as statutes, regulations, rulings, court opinions, as well as secondary resources such as dictionaries, directories, and law reviews. It also includes tips on researching and writing about the law.

Getting Started

These are some of the most popular sources for legal research.

Overview of the American Legal System

The Three Branches of Government

Separation of powers: The United States government is divided into three branches, each with its own distinct powers independent of the other two. 

  • The Legislative Branch makes the laws, called statutes [statutory law]. The Legislative Branch consists of the United States Congress, which is divided into two chambers: the Senate, in which each state is represented by two members, and the House of Representatives, in which states are represented proportionally according to their population.
  • The Executive Branch administers and enforces the laws, indicating through regulations and rulings exactly how the statutes are to be carried out [administrative or regulatory law]. The Executive Branch consists of the President, the Vice President, the Cabinet and all federal Departments, and most federal agencies.
  • The Judicial Branch interprets the meaning of the laws through court opinions [judiciary law]. The Judicial Branch consists of the Supreme Court, which mainly reviews cases appealed from lower courts and is the court of last appeal in the United States; the Federal Circuit Courts of Appeals, which hear appeals of contested decisions from the District Courts; the District Courts, which are federal trial courts; and several Special Courts that hear special types of cases, such as international trade cases or cases against the federal government.

Checks and Balances: Each branch has the authority to counter the actions of the other branches in certain ways, so that no one branch has complete control over the government. For example, the President may veto a bill passed by Congress and has the power to appoint federal judges; Congress must approve presidential appointments, and has the power to impeach federal judges and other officials; and the Supreme court can declare laws passed by Congress or regulations issued by the Executive Branch to be unconstitutional. 


The U.S. federal government has jurisdiction over matters that are of national interest or that cross state boundaries, such as the currency system. The state governments reserve authority over matters that transpire within their own boundaries, such as punishment for various crimes.

In case of a conflict, federal laws and international treaties supersede state and local laws.

The U.S. Constitution, considered the supreme law of the land, supersedes all federal, state, and local laws. None of these laws is allowed to contradict the Constitution. Each state also has its own constitution, which laws within the state cannot contradict.

Each state government also has its own constitution and its own three branches of government. The legislative branch consists of a state legislature, usually consisting of a senate and a house of representatives, which enacts the statutes that apply to that state. The executive branch consists of a governor and various state agencies, implement the state laws and prescribe how they are to be carried out. The judicial branch consists of a hierarchy of courts, including several trial courts, at least one level of appellate courts, and one or two courts of last resort. State courts only interpret laws within their own state, and their opinions are not binding on other states.

Judicial Law

State Law

Statutory Law

Regulatory Law

How to Read a Legal Citation

In the 1920s, editors of law reviews realized that the extensive footnotes to the scholarly article in their publications often took up more space than the articles themselves. In order to simplify matters and economize on space, they devised a shorthand system for identifying legal publications. This system was codified in the 1926 publication A Uniform System of Citation, which came to be known as The Bluebook. This system is now the most widely used method for citing legal materials in the United States.

For citations to Texas law, the Texas Law Review Association has developed a supplement to The Bluebook called Texas Rules of Form. It is popularly referred to as the Greenbook. The rules in the Greenbook apply specifically to sources of Texas state law and always supersede the general rules contained in the Bluebook. The Greenbook is not available online, but a paper copy is on reserve at the Government Documents Service Desk.

More a more thorough explanation of legal citation principles, including instructions on how to create a citation, see Basic Legal Citation by Peter W. Martin of Cornell University.

Example of a Legal Citation

Empy v. State, 571 S.W.2d 526 (Tex. Crim. App. 1978).

This is a reference to a case between Louis Empy and the state of Texas. The decision was published in volume 571 of the South Western Reporter, second series, on page 526. The case was tried in 1978 in the Texas Court of Criminal Appeals.

For more examples of various types of legal materials, see Basic Legal Citation: Examples.

Basic Form of a Citation

The exact format of a legal citation will differ depending on what sort of work is being cited. Nevertheless, legal citations following The Bluebook will include the following elements:

  • The name of the case, statute, regulation, or article
  • The source information, which consists of three parts:
    • Volume number
    • Name of the source (usually abbreviated)
    • Page or section number
  • The date

Many citations contain additional information, such as an author's name or the name of the court that issued a particular decision. This can help you evaluate how authoritative or credible the item cited might be.


Abbreviations are used to make a citation as brief as possible. They can also render it obscure. There are many resources that can help you identify what source is being referred to by an abbreviation in a legal citation. Perhaps the most comprehensive is Bieber's Dictionary of Legal Abbreviations, by Mary Miles Prince. This reference work is available at the Government Documents Service Desk in Willis Library.


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