All 435 seats in the United States House of Representatives are up for election Tuesday night as Democrats and Republicans vie for control of the lower chamber of Congress. Representatives are elected to two-year terms and serve a specific district in their state. The number of representatives per state is set by that state's population.

Republicans currently hold the majority in the House, while Democrats have the Senate. A handful of tight matchups could swing the balance of power.

The US Congress is often referred to as a single entity, but it is a combination of the House of Representatives and the Senate. Here are the differences.