The Constitution defines the fundamental law of the United States federal government, setting forth the three principal branches of the federal government, outlining their jurisdictions, and propounding the basic rights of U.S. citizens. It has become the landmark legal document of the Western world, and is the oldest written national constitution currently in effect. The essential principle of the document is that government must be confined to the rule of law.

Twenty-seven amendments have been added to the Constitution since 1789. The first ten amendments, known as the Bill of Rights, were adopted as a unit in 1791.

Although the federal government is required by the provisions of the Constitution to respect the individual citizen's basic rights, such as right of trial by jury (Article I, Sec. 9), the most significant guarantees for individual civil rights were provided by ratification of the Bill of Rights (Amendments 1-10). The First Amendment guarantees freedom of religion, speech, and the press, the rights of peaceful assembly and petition. Other amendments guarantee private property, fair treatment of those accused of crimes, such as unreasonable search and seizure, freedom from self-incrimination, a speedy and impartial jury trial, and representation by counsel.