The United States Congress is made up of two distinct houses: the Senate and the House of Representatives. The Senate is made up of 100 senators, two from every state, who are elected to the Senate every 6 years on a rotating basis, meaning that 1/3 of the Senate is up for election every 2 years. The House of Representatives features 435 members who are elected every 2 years.
Combined, the House of Representatives and Senate make up what is known as Congress, which is the legislative branch of the government, and 1/3 of the nation's ruling body. The other two parts are the judicial branch, which includes judges and the courts system, and the executive branch, which features the President and his cabinet.
There are no limits as to how long a senator or house member may hold office. In the case of a Congressman or Congresswoman's death or ouster from office, special elections are usually held to replace the Congress member to maintain the total membership.
The number of House of Representatives members that a state has is determined by the state's population. For example, smaller states and districts, such as Delaware, the District of Columbia and Montana, only have one House representative. Larger states have many more, such as California with 53 and Texas with 36.