The names of the finalists will be announced in Sao Paolo, Brazil, on 29 November. The overall winner will be announced in January 2013.
So far the most likely winner is Barcelona's Lionel Messi, who has won the Ballon d'Or three times already and is the current winner. If he wins he will be the first player ever to do this four times in a row. Another strong possibility is Cristiano Ronaldo of Real Madrid, who won in 2008. You can see the full list of nominees here.
Until 2010 the Ballon d'Or and the FIFA World Player of the Year were separate awards. The Ballon d'Or was founded in 1956 by French sports writer Gabriel Hanot, who started it by asking other journalists to vote for the player they thought the best, in Europe. There is still a Europe-only award called the UEAFA best Player in Europe Award, created in 2011.