Though formatted differently from the original 58-volume series which continued under Grosset & Dunlap's control, these new books were published under the Hardy Boys Mystery Stories banner.
After volume 85, the series took a two-and-a-half-year hiatus due to the sale of the Stratemeyer Syndicate to Simon & Schuster.
At this point, book packager Mega-Books took over the series, and hired different ghostwriters for the job (many of whom are still unknown).
With the reboot of Nancy Drew into Girl Detective, coupled with declining sales, Simon & Schuster ended the original series in April 2005.
The Hardy Boys Casefiles are aimed at early-to-mid teen readers and have more mature themes, including espionage, murder, and slight romance.
The new direction the series would take was set in the first volume, Dead On Target, as a bomb planted in the Hardy Boys' car blows up Joe's longtime girlfriend, Iola Morton, in the first chapter.
This series was published in mass-market, or rack-sized, paperbacks to widen the distribution of the books to supermarkets and other outlets.
In September 1987 the Hardy Boys Digest series was revived and continued with #86 The Mystery of the Silver Star.
Events from the Casefiles are not referenced in the Digest series, and Iola Morton is alive and connected with Joe Hardy as in the previous 85 titles.
Several spin-off series were cancelled by Simon & Schuster at the end of 1997, including The Hardy Boys Casefiles.
This series follows the formula of the main characters and their friends typically involved in separate mysteries that end up being connected.
Subsequent books focus on the respect and friendship that developed between the two and their continued feelings for Ned Nickerson and Callie Shaw.
In 2005/06 Simon & Schuster UK reissued four Casefiles under the Undercover Brothers label, with two other books being planned but cancelled before publication.
Spy Set - box set of volumes 1–4 (2005) The Nancy Drew and the Hardy Boys Super Mystery books are a new series first published in June 2007 and are not to be confused with the Nancy Drew and Hardy Boys SuperMystery series that was published between 1988 and 1998.
Series was cancelled with Nancy Drew: Girl Detective and The Hardy Boys: Undercover Brothers in 2012.
The reboot series publishes two to three new titles a year in paperback, hardcover book with dust jacket, and as eBooks.
The Hardy Boys Secret Files is a series begun in 2010 by the publisher Simon & Schuster under their Aladdin imprint.