The significance of the U.S. Constitution in American government lies in its role as the supreme law of the land, establishing the framework for federal governance and protecting individual rights. Ratified in 1788, it outlines the structure of government, dividing power among the executive, legislative, and judicial branches, each with checks and balances to prevent abuse of power. Additionally, it enshrines fundamental rights through the Bill of Rights. The Constitution has been instrumental in promoting democracy and has served as a model for numerous other nations' governance structures, reflecting its enduring influence.