The U.S. Senate is comprised of two senators from each state, so there are 100 members of the Senate as of 2014. Residents of Washington D.C. are the only U.S. citizens who do not have representation in the Senate.
A senator must be at least 30 years old, a resident of the state that she represents, and a U.S. citizen for at least 9 years. Senators serve a term of six years, and Senate elections are held in two-year intervals. This means that approximately one-third of the Senate seats are up for election every two years. The number of senators is not dependent upon the state's population.