The U.S. Constitution mandates equal representation in the U.S. Senate from each state. Voters in each state elect two senators. As of 2015, there are 100 members of the U.S. Senate.
A member of the U.S. Senate serves a six-year term. These terms are staggered, leaving roughly one-third of the body's members up for election every two years. In order to serve in the U.S. Senate, an individual must be 30 years of age or older and a citizen of the United States for nine years. Additionally, senate candidates must be a resident of the state in which they run for office.