Members of the United States Senate serve 6-year terms, but start their terms in staggered starts so that roughly one-third of the Senate body starts with fresh representatives every 2 years. As established in the Constitution of the United States, each state receives equal representation in the Senate. Each state sends two senators to the Senate, creating a total of 100 representatives at all times.
Senate members, like other public officials, must meet several qualifying criteria to be considered for election. They must be at least 30 years old at the time of Senate elections, and be residents of the states they represent. Potential Senate members must also be citizens of the United States for at least 9 years to be eligible for election.
The Senate election process, like that for other official elections in the United States, follows a formal schedule. Citizens vote for candidates in even years; votes take place on the first Tuesday in November. In each election, senators earning the majority vote, also called the popular vote, secure their spots in the Senate.
Sometimes Senate appointments lead to mid-term vacancies. If that happens, Senators' states follow procedures for finding replacements. States may have their own methods for selecting a fill-in candidate, but nevertheless must make appointments quickly to ensure the Senate membership remains at an even 100.