1. Article I, Section 3 of the Constitution: 1) each senator must be at least 30 years old, 2) must have been a citizen of the United States for at least the past nine years, and 3) must be (at the time of the election) an inhabitant of the state they seek to represent.
2. Senators make $174,000 per year (2009). They have the exact same health and retirement benefits as other federal employees.
3. The Senate may expel a senator with a 2/3 vote.
4. The District of Columbia and all other U.S. Territories do not have representation in either House of Congress.
5. Senators are elected in staggered terms. Approximately one-third of the senate seats are up for election every other year. This prevents states from having two senate vacancies at once.