Young Adult Literature
With its whimsical illustrations, adorable main characters (tiny mice with big ears!), and fairy tale qualities, The Tale of Despereaux is definitely geared towards young readers. The story gets dark at times with all its death and revenge, but in the end, the characters still live happily ever after. It's a tale of good and evil, of friendship and beautiful princesses—with some great life lessons thrown in for good measure. What more could a kid ask for?
Fantasy
The Tale of Despereaux is obviously fantastical in that it takes place in a place that does not exist—the Kingdom of Dor—and involves princesses and talking rodents. The animals in the story are all as smart as can be, can talk to humans, and can even read books without proper schooling. Now that's what we call magic.
Quest
In the book, Despereaux is on a personal quest to save the princess. As the hero of the story (and as a mouse who sees himself as a knight in shining armor), Despereaux has to overcome obstacles, face off against terrible creatures, and find Princess Pea in order to deliver her back to the light-filled world of the castle. He achieves his mission at the end and is rewarded with the princess' friendship and free run of the castle. And all the soup he can eat.