Consdtudons are the framework for government and may limit or define the powers of political bodies. The U.S. constitutional law is the written text of the state and federal consdtudons. It is also the product of judicial interpretation of the U.S. Consdtudon in response to the constitutional issues in cases that come before the courts. For example，constitutional law usually comes firom judges* interpretation of the meaning of vague or general phrases in the Constitution, such as "due " U.S. Constitution Amertan Society and DJLre process of law" or unreasonable searches and seizures". So, it is the decisions by judges, who interpret and apply particular constitutional provisions and principles to specific cases, that create constitutional law. In deciding their cases, courts look to these constitutional provisions and principles for guidance. Once a court has interpreted a constitutional provision in a certain fashion, it becomes a precedent. Under this doctrine, the judicial branch is required to stick to existing precedent in all future cases presenting similar drcumstances, unless it has a unique reason for deviating from the precedent or overruling it Over dme these precedents accumulate to become a body of case law.

In the United States, the Supreme Court plays a central role in developing constitutional law. In 1982，for instance, the Court decided in United States v. Ross that the Fourth Amendment ban against “unreasonable searches and seizures'，did not prevent police, under certain circumstances, from searching the contents of a car without a search warrant. Thus, the development of American constitutional law is based on the power of the Supreme Court to consider whether particular federal and state laws and executive actions are consistent with the Constitution. Consequently, the power of judicial review and the principle of constitutionalism are fundamental factors in the development of constitutional law by the judicial branch of government.

The Common Law

The common law refers to the system of laws originated and developed in England and based on court decisions, on the doctrines implicit in those decisions, and on customs and usages rather than on codified written laws. The United States, as well as most Commonwealth countries, is an heir to the common law legal tradition of English law. In all U.S. states except Louisiana, the common law is the law of the state to the extent that it is not inconsistent to domestic law or local conditions.

However, it is important to understand that much of contemporary American common law has diverged significantly from British Commonwealth common law. The reason is that althou^i the courts of the various Commonwealth nations arc often influenced by each other’s rulings, American courts rarely follow post -Revolution Commonwealth rulings unless there is no American ruling for that matter.