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Sources of Law

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The primary sources of law in the United States are the United States Constitution, state constitutions, federal and state statutes, common law, case law, and administrative law.


Constitutions define how governments are to be organized, and the power and responsibilities of those governments. Constitutions can also serve to protect individual liberties. For example, in the federal Constitution, the first 3 Articles are devoted to laying out the structure and scope of the federal government, while the First 10 Amendments (the “Bill of Rights”) are primarily devoted to protecting individual liberties. Because a constitution is the blueprint for the entire government, everything that the government does must be consistent with the Constitution. If any action taken by any part of the government is inconsistent with the Constitution, that action is said to be "unconstitutional" and it must be struck down.


Statutes are created by the federal, state and local legislatures, which are comprised of elected officials who have the power to create laws. Courts must apply statutes, if available, to the facts of a case. If no statute exists, courts defer to common law or case law. Common law refers to law that has not actually been codified or passed by a legislature, but is nonetheless applied by courts based on tradition and the legal history of the United States and even dating back to the legal system in England. Case law refers to law that comes directly from court decisions. "Case law" consists primarily of judicial interpretations of the Constitution, a statute or the common law. "Case law" includes Supreme Court and lower court decisions.

Because statutes are passed by legislatures who are empowered to make laws, statutes control over common law or case law where the two conflict. An exception to this is that a statute can be thrown out by a court if, under interpretations made by applicable case law, the statute is unconstitutional (inconsistent with the Constitution). 

The process through which an idea becomes a law is long and complicated. Although the federal and state procedures can be technically quite different, they are, at their most basic levels, similar. 

First, a lawmaker introduces a bill in either the Senate or House of Representatives (or their equivalents at the state level). After the bill is introduced, it is reviewed by the appropriate committee and/or subcommittee. The subcommittee reviews the bill, holds hearings and makes amendments that it deems necessary. Once the subcommittee is satisfied with the bill, it presents the new version to the full committee. If the full committee approves of the bill, the bill goes to the full chamber in which it was originally introduced (Senate or House), for debate and final vote. 

If the first chamber passes the bill, the bill is presented to the other chamber, where it is reviewed in similar fashion. Both chambers must approve the bill in identical form. If the bill is not approved by both chambers, it may be sent to a conference committee to resolve issues where the chambers disagree. 

Once approved by both chambers, the bill is presented to the President (or Governor) for signature. Once signed, the bill becomes a law and is effective, as the legislature has prescribed. The President or Governor can also refuse to sign the bill, an action known as a "veto." This prevents the bill from becoming law, although vetoes can often be overridden by supermajority votes by the legislatures (under the federal system, a 2/3 majority of both houses of Congress is required to override a presidential veto). The federal government and many state governments have provisions whereby if the President or Governor does not sign the bill within a certain number of days while the legislature is in session, the bill automatically becomes a law.

For more information on how laws are passed under the federal system, see: 
HOW OUR LAWS ARE MADE, Revised and Updated by Charles W. Johnson, Parliamentarian, United States House of Representatives, January 31, 2000

When enacted, statutes, at both the state and federal level, usually contain the following sections: preamble, definitional, procedural, substantive and construction. 

The preamble is simply a policy statement that explains why the law has been passed and the reasoning behind the passage of the law. The definitional section defines key terms within the bill. The procedural section illustrates how and when the law is intended to take effect. For example, the section might state that the law will only last for 10 years from the date of its passage. The substantive section lays out the terms for the law itself (this is the “meat” of the law). The construction section spells out general guidelines the courts should use in interpreting the law. 

Note that not all of these sections will appear in any given law. The only section that is absolutely necessary and that appears in every bill is the substantive section, as it is that section that delineates the actual law(s) that the legislature is enacting.

Court Interpretation 

Because legislatures cannot write laws for every possible factual scenario, laws are written broadly enough to be applicable to a variety of situations. To what situations a law may apply, however, is not always clear. This is when courts must engage in statutory interpretation to determine the legislature’s intent. There are many things courts will consider:

Binding precedent: If a court with direct appellate jurisdiction over the court considering the issue (i.e., a court to whom cases can be appealed to from that court) has interpreted the law in a certain manner, that interpretation must be used by the court.

Actual language: Most legislation is the result of careful planning and consideration. Therefore, courts give great deference to the actual words the legislature has chosen to use.

Legislative history: When the language is ambiguous, courts will often review the statute’s legislative history, if available. As explained above, statutes are usually debated before passed; these debates are often recorded. Committee and subcommittee reports are included in the legislative history. Recent legislative history is readily available at the federal level; at the state level, however, it can be quite sparse.

Context, general and specific: Courts will often consider the context in which the statute was enacted, its purpose, and other existing statutes that may be similar. Why the statute was enacted at the time it was enacted may also be important in determining public policy.

Treatment by other courts: If the statute has not been construed or interpreted by the appellate courts, no precedent binds the trial courts. Other trial courts, however, may have considered the same issue; these decisions may be helpful to the court currently considering the issue, and the court will often review other similar decisions. These decisions may be from the same jurisdiction or a different jurisdiction, although decisions from foreign jurisdictions are less persuasive. Where an appellate court is considering an issue for the first time, it may also review other courts’ decisions, even if they are from other jurisdictions.
Legal treatises and other scholarly literature: Because statutes are often analyzed by legal scholars before they are considered by the courts, many courts find such analysis helpful in their own interpretation.

Common law: Where a statute codifies a principle of the common law, decisions analyzing the common law may be helpful.

Other jurisdictions’ statutes: Many states have similar legislation to each other on numerous topics. A review of similar legislation in other states may shed light on the legislation in question.

Administrative Law

As regulation becomes more pervasive, the body of Administrative law has become increasingly important. Administrative law refers to the regulations created by administrative agencies

Administrative agencies are created by the legislature by what are called “enabling” statutes. The administrative agencies are part of the executive branch and are charged with the administration of government functions. 

EXAMPLE: Congress has charged the Environmental Protection Agency (“EPA”) with the protection of the environment, and Congress has also enacted legislation concerning the environment, such as the Clean Air Act and the Clean Water Act. It is up to the EPA to enforce those laws as created by Congress. Congress has also allowed the EPA to create its own regulations to enforce legislation Congress has enacted. For example, if Congress enacted legislation that mandated that all motor vehicle emissions be reduced by 30% by 2010 and authorized the EPA to determine how to achieve such a goal, the EPA would write specific regulations to ensure compliance with the law. These regulations would then have the full force of federal law behind them. States have similar administrative agencies.

A person aggrieved by an agency’s decision can usually appeal to an appellate tribunal (court) within the agency. One may often appeal the appellate tribunal’s decision to a federal or state court.

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