In the United States presidential elections are held every four years.
Congressional elections take place every two years.
Elections for state and local office usually coincide with national elections. While there are a range of political parties to choose from, the two party system is a solid feature of American politics. The Republican and Democratic parties, by virtue of tradition and their vast resources, dominate the presidential selection process. Native-born or naturalised US citizens over the age of 18, with the exception of convicted felons, have the right to vote. But the President is actually elected by the electoral college and not directly by the population.