Interactive gamers are awaiting the holiday 2012 release of Halo 4 from 343 Industries and Microsoft Game Studios; it’s the latest in one of the all-time bestselling videogame series. The Halo franchise, which encompasses games, publishing, and merchandise, has generated nearly $3 billion in retail sales worldwide since 2001.

One key component of the franchise is Tor Books’ series of 11 licensed novels, including eight published since 2006 and another three originally released by Del Rey, starting in 2001, which Tor has reprinted in updated editions. All told, the 11 books have sold 2.7 million units.

“The Halo universe is so vast,” says Tor editor Stacy Hill. “It’s a real sci-fi epic, with broad appeal, and there are lots of good stories to be told.” Current Halo releases from Tor include the Kilo-Five trilogy by Karen Traviss, an action-heavy military fiction series, and the Forerunners series, a high-concept sci-fi trilogy by Greg Bear. Other Halo authors have included Eric S. Nylund, William C. Dietz, Joseph Staten, and Tobias S. Buckell.

Hill believes the books’ primary appeal is to gamers. “But when we use writers like Greg Bear, you also get Greg Bear readers to try them out. A book in the Forerunners series is very much a Greg Bear book.”

“One thing I found surprising, but very cool, is that parents and librarians often ask for copies of these,” Hill continues. “They’re great gateway books for kids.”

Other Halo publishers include Marvel (graphic novels), DK (reference), Titan (“Art Of”), and Brady Games (strategy guides).