The U.S. legal system rests upon the principle that the fundamental purpose of government is to protect the inherent rights and freedoms that belong to all people, and to ensure equal treatment for all.

In the United States, these rights and freedoms are embodied most explicitly in the first 10 amendments to the Constitution, known as the Bill of Rights, ratified in 1791, and in the "equal protection" clause of the 14th Amendment, ratified in 1868, after the Civil War. Over its history, a great body of statutory law, court decisions, and regulatory procedures have evolved and elaborated the freedoms and rights set out in the Bill of Rights and other provisions of the Constitution.

The First Amendment protects freedom of speech and religious worship. It also protects the right of people to organize and protest peacefully for political or social change.

Freedom of speech and of the press is a cornerstone of any democracy. For that reason, the First Amendment prohibits the government from attempting to control or monitor the content of public statements or reports in the press — resting on the conviction that, in the end, open debate will leader to greater truth and wiser public decisions. Only in rare and very limited situations can written or spoken speech be limited or punished.

Religious freedom means that the state cannot sponsor, support, or discourage religious expression by any group or individual. Religion remains a prominent feature of life in the United States, but courts have held that the First Amendment means that a "wall" must separate religion and the government.

The Second Amendment, which protects the right to bear arms because a "well regulated militia" is necessary for the security of the state, remains controversial. Some believe that it means that an individual's right to bear arms is protected by the Constitution; others assert that it only gives each state the right to maintain its own "militia," known today as the National Guard. The Supreme Court has not provided any definitive pronouncement on the interpretation of the Second Amendment.

Americans are protected against unreasonable searches and seizure of their property and person. For example, an individual cannot be arrested merely on the suspicion of the police. Moreover, evidence seized during an illegal search, or evidence derived there from, cannot be used as evidence in a trial.

In modern times, with changes in technology and culture, this protection has been expanded into a broader constitutional right of privacy — an example of extrapolating an implied right from the express words of the Constitution itself.

Several amendments protect persons accused of crimes, designed to ensure, broadly speaking, "due process of law." The accused have a right to a speedy and public trial in which they are judged by a jury of their peers, and in which they have the opportunity to confront their accusers. They cannot be forced to incriminate themselves by testifying at trial. The Eighth Amendment also explicitly outlaws "cruel and unusual punishment." Criminal suspects are entitled to legal counsel, which is reflected in the well-known Miranda warnings that the police give persons under arrest, restating basic rights against self-incrimination ("You have the right to remain silent. Anything you say can and will be used against you in court of law") and due process of law ("You have the right to an attorney. If you cannot afford an attorney, one will be appointed for you").

The accused cannot be tried for the same crime twice (double jeopardy), and cannot be tried for actions that were not crimes at the time they were committed (ex post facto laws).

The Constitution protects property rights as well. For example, government at any level must meet stringent legal requirements, and pay just compensation, before it can take anyone's private property, and it may take private property only for “public use,” not private purposes.

The 14th Amendment's guarantee of "equal protection of the laws" has served as a legal foundation for the social and political movements of the 20th century to secure equal rights for women and for African Americans and other minority groups.

Other amendments, including the 15th (voting rights regardless of race), 19th (women's right to vote), 24th (abolition of poll, or election, taxes), and 26th (lowering voting age to 18) reflect the struggle to ensure the constitutional right to vote and participate in the political process for all citizens.

The rights embodied in the Constitution do not exist in isolation or in the abstract. They require recognition and active support by all Americans, regardless of political views or position in society. Some obligations, notably serving on juries, can be required by law. Most forms of participation in the life of the community and nation, such as voting, are voluntary, yet critical to the healthy functioning of American democracy and protection of the rights and freedoms of the people.

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