The major document outlining the principles of the U.S. government is the Constitution, ratified in 1788. This foundational document structures the federal government and establishes the rights of its citizens. It embodies the principles of separation of powers, checks and balances, and federalism, ensuring that no single branch of government holds unchecked power. The Bill of Rights, added shortly after ratification, enumerates individual liberties, reinforcing the protection of personal freedoms. The Constitution remains a living document, subject to amendments and interpretations, guiding the U.S. legal and political systems.