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 are vying to keep control of the lower chamber, while Democrats hope to flip enough seats to take over. There are about two dozen tossup House races, where either party could come away with the win regardless of incumbency,

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.