The United States is a republic, which means that the people choose leaders by voting in elections, and those leaders run the government. It is a constitution-based federal republic, in which the Constitution is the highest law and power is shared between the national (federal) government and the state governments. 

It is also a representative democracy, because people do not vote on every law themselves (sometimes they do – when a referendum is called on a specific, particularly important issue); they elect representatives (such as members of Congress, the President, state and local officials) to make laws and regulations for them.