National Treasure: Book of Secrets is a 2007 sequel to the 2004 film National Treasure. It will be directed by Jon Turteltaub and written primarily by Gregory Poirier. Jerry Bruckheimer is the producer of the film.
It was stated in the first film's commentary that there were no plans for a sequel, but, due to the first film's impressive box-office performance, an earning of $347.5 million worldwide, a sequel was given the go-ahead in 2005.
The film will be released on December 21, 2007.

 

Source: Wikipedia