Because the United States is a democratic republic, its citizens have the ability to vote for leaders to represent them. The United States holds general elections in November of every even-numbered year. These general elections typically include presidential elections and congressional elections -- for the U.S. Senate and House of Representatives -- along with state and local elections. There are a number of key differences voters should be aware of between presidential and congressional elections.

Election Cycles

U.S. representatives serve two year terms, senators serve six year terms and the president serves a four year term. Thus voters elect a member of Congress to represent them in the House of Representatives every general election. One-third of the Senate faces re-election in any given general election. Presidential elections are held every other general election. General elections in which voters are not voting for president are called mid-term elections.

Who Can Vote for Whom

All U.S. citizens 18 and older are allowed to vote in U.S. presidential elections, unless they have lost voting privileges according to state or federal laws. Voters can also vote for their choice for U.S. Senate if one of their state's two Senate seats is scheduled for an election. Congressional districts for the House of Representatives are drawn by state legislatures based on population distribution. Because this process is controlled by state legislatures, districts are often drawn up in a way that favors the party that controls the state's legislature. Voters may only vote in congressional elections for the congressional district in which they live.

Electoral College vs. Direct Election

Senators and representatives are elected by direct election. Whichever candidate gets the most votes in his state or district wins the election and assumes the office to which he has been elected. The presidential election is a bit more complex, using a mechanism known as the Electoral College to select the president. Each state has a number of electoral votes in the Electoral College equal to its number of senators and representatives in Congress. Most states grant all of to the presidential candidate who wins the state's popular vote. Nebraska and Maine split their electoral votes according to the percentage of voters who voted for each candidate. Whichever presidential candidate receives the most electoral votes becomes the next president.

Special Elections vs. Appointments

If the president of the United States doesn't complete a full term in office, whether due to death, resignation or impeachment, the vice president assumes the office of the presidency for the remainder of the term. No special elections are held. When a senator fails to complete a term, the state's governor may appoint an interim replacement or may call for a special election, depending on the state's laws. When a seat is vacated in the House of Representatives, the governor of the state represented may call for a special election to fill the vacant seat or may leave the seat vacant until the next general election. Generally, the seat is only left vacant if there is not enough time for the election process before the next session of Congress.