The Hardy Boys: Undercover Brothers is a detective fiction series of books published by Aladdin Paperbacks (an imprint of Simon & Schuster), which replaced The Hardy Boys Digest paperbacks in early 2005.^[1] All the books in the series have been written under the pen name of Franklin W. Dixon.

The Undercover Brothers is about two teenage brother detectives, Frank and Joe Hardy, who are the sons of world-famous PI Fenton Hardy. Although there are many similarities in this series to the previous Hardy Boys series, there are also many changes, for example:

• The Hardy boys are undercover agents for American Teens Against Crime (ATAC), a top-secret government organization, co-founded by their father, and are solving more realistic and violent crimes.^[1] Since it is a top-secret organization, Frank and Joe often need to make up excuses to convince their mother and aunt to let them go to places.
• The books in this series are written in a first-person narrative style with Frank and Joe alternating chapters and often interrupting each other.^[1]
• The Hardy boys' aunt's name is shortened from Gertrude to Trudy. It is revealed in Hurricane Joe why she shortened her name to Trudy. This version is much younger than the character in other Hardy Boys series.
• The Hardy boys' long-time girlfriends, Callie Shaw and Iola Morton, appear in the books, but only as platonic friends of the boys instead of love interests. Other friends from the original series are occasionally mentioned but never play important roles as they did in the past.
• The Hardys have a pet parrot named Playback.^[2]

The Hardy Boys Secret Files is a series begun in 2010 by the publisher Simon & Schuster under their Aladdin imprint. It features the Hardy Boys, Frank and Joe, as grade-school detectives. Three new titles are published yearly as paperback books and eBooks. This series ended in 2015 and was replaced by the Hardy Boys Clue Book series.

1. Trouble at the Arcade
2. The Missing Mitt
3. Mystery Map
4. Hopping Mad
5. A Monster of a Mystery
6. The Bicycle Thief
7. The Disappearing Dog
8. Sports Sabotage
9. The Great Coaster Caper
10. A Rockin' Mystery (October 2012)
11. Robot Rumble (April 2013)
12. Lights, Camera...Zombies! (August 2013)
13. Balloon Blow-Up (December 2013)
14. Fossil Frenzy (April 2014)
15. Ship of Secrets (August 2014)
16. Camping Chaos (December 2014)
17. The Great Escape (April 2015)
18. Medieval Upheaval (August 2015)
19. The Race Is On (December 2015)

In the spring of 2005, NBM launched its new imprint, Papercutz, with the publication of two three-part comic book series; Nancy Drew (The Demon of River Heights) and The Hardy Boys (The Ocean of Osyria).^[3] After the completion of both series, The Demon of River Heights series and The Ocean of Osyria series were both collected into 92 pages graphic novels, becoming the first titles in the Nancy Drew graphic novel series and the Hardy Boys graphic novel series respectively.

All other titles in both series have been made in graphic novel format only and are published every three months.

• The Hardy Boys