One hundred members make up the United States Senate each year, with every state represented by two senators. In order to become a United States senator, a person must be a citizen of the United States for at least 9 years and must be over the age of 30.
A senator serves for 6 years at a time and must be elected to the position. Voters elect senators every 2 years; however, just 1/3 of the senate population is "elected every 2 years," according to the United States Senate site. The United States Senate site offers profiles and biographies on many of the most prominent senators, as well as full membership lists, including the Membership of the 114th Congress.