The United States Constitution is the cornerstone of federal law in the United States. It describes the three chief branches of the Federal Government and their jurisdictions, and lays out the basic rights of citizens of the United States. The U.S. Constitution is the oldest Federal constitution in existence and was framed by a convention of delegates from twelve of the thirteen original states in Philadelphia in May 1787, Rhode Island failing to send a delegate. The U.S. Constitution is the landmark legal document of the United States.