Every year, five new members are elected to the UN Security Council, which has 15 members in all.
Ten of the UN SC members are “non-permanent”; and serve just two years. Half of those are replaced annually.
Today, Burkina Faso, Costa Rica, Croatia, Libya and Viet Nam were elected to serve two-year term starting on 1 January 2008 … They will replace Congo, Ghana, Peru, Qatar and Slovakia, whose two year terms expire on 31 December this year.
http://www.un.org/apps/news/story.asp?NewsID=24304&Cr=security&Cr1=council
The UN Security Council also has five permanent members: the U.S.A., Russian Federation, China, U.K., and France.