* Adventure: The series focuses on the thrilling adventures of the Cahills as they race around the world to find clues and outwit their rivals.
* Mystery: Each book features a central mystery involving the 39 Clues and the Cahills' family history.
* Historical fiction: The series incorporates real historical events, figures, and locations, often weaving them into the narrative.
* Fantasy: The books often feature elements of magic and the supernatural, especially in the later books.
Overall, the 39 Clues series can be described as adventure-mystery with historical elements and some fantasy.