Law can be thought of as the total of all the rules governing behavior that is enforceable in courts. There are four sources of law in the United States including the U.S. Constitution, state and federal statutes, administrative law, and court made law or common law. This article provides a brief overview of these various sources of law.


U.S. Constitution

In order to understand the complexity of the American legal system it is helpful to recall that the United States was founded as the union of 13 colonies, with each one claiming independence from the British Crown. In 1787, the U.S. Constitution was put in place to govern the relationship among the 13 colonies and the national Congress. It defined the powers and authority of the federal and state governments and delineated the kinds of laws that the federal Congress and the state legislatures could pass.

The U.S. Constitution is often referred to as the “Law of the Land” because it supersedes all other laws or rules. The power of Congress and of the state legislatures to pass laws is always subject to the U.S. Constitution. Laws or rules that are inconsistent with the Constitution either because they violate rights guaranteed by the Constitution or because the Constitution does not authorize that legislature to pass that kind of law are unconstitutional. A court that finds a law to be unconstitutional will strike it down giving it no force or effect.


As previously stated, the Constitution gives Congress and state legislatures the power to pass legislation or laws in certain domains. Federal and state laws are known as statutes. The powers of Congress, or the federal legislature, to pass laws are set out in Article I of the Constitution. Examples of domains for which Congress has jurisdiction and can pass statutes include laws related to providing and maintaining a Navy, establishing post offices, and regulating commerce with foreign nations.

All powers not expressly granted to the federal legislature by the Constitution are reserved for the states. State legislatures h

ave the power to pass laws concerning many domains of interest to forensic psychologists. For example, state legislatures have the power to enact legislation regarding criminal law, civil commitment, and family law. With respect to domains within their jurisdiction, each state will have its own statute or statutes. For example, California has enacted The Penal Code of California while Michigan has enacted The Michigan Penal Code – both statutes dealing with criminal law within their jurisdiction.

Administrative Rules and Regulations

In some cases, the federal or state government may delegate some of its powers to specialized administrative agencies through authorizing statutes. As a part of this delegation, many of these agencies will have the authority to make rules and regulations relevant to their responsibilities and within their area of expertise. These laws are referred to as rules or regulations rather than statutes, but they generally have the same force as statutes. The power of the administrative agency to enact rules and regulations is set out in the authorizing statute. One area of administrative law relevant to forensic psychologist is the laws surrounding the determination of disability and disability benefits.

Common Law

The American legal system has its roots in the English common law system. Historically, English grand juries, kings, and magistrates catalogued their decisions according to the type and subject matter of the case. When subsequent cases came before them, they reviewed earlier decisions to determine whether a previous case was sufficiently similar to the current one. If so, they applied the principles set out in the earlier decision to the new decision. This body of principles came to be known as the common law. The common law is therefore often referred to as court– or judge– made law. Many of the principles established in English common law continue to be applied by American courts today. In addition, the doctrine of stare decisis, Latin for “let the decision stand,” remains. That is, where a judge interprets a law, subsequent judges will often be bound by that interpretation through the process of precedence. Whether a judge is bound by a previous decision will largely depend on the jurisdiction of the court.

Excerpted from: Roesch, R., Zapf, P. A., & Hart, S. D. (2010). Forensic psychology and law. Hoboken, NJ: Wiley.