What type of book is Geronimo Stilton?

* (for a complete list see the related link below)

Latest titles in the book series:

#44: The Giant Diamond Robbery (January 2011)

#45: Save the White Whale! (April 2011)

#46: The Haunted Castle (July 2011)

#47: Run for the Hills, Geronimo! (October 2011)

#48: The Mystery in Venice (January 2012)

Graphic Novels:

#8: Play it Again, Mozart! (September 13, 2011)

#9: The Weird Book Machine (January 31, 2012)