This past June, The New York Times Best Seller List for mass-market paperbacks featured an outlier among its usual list of suspects. After Inferno by Dan Brown and several books in George R.R. Martin’s A Song of Fire and Ice series, sat a book adaptation of the blockbuster film Godzilla, written by Greg Cox.

Cox’s book is what’s known in the business as a movie “novelization.” The term means exactly what you think it does: it’s a novel based on a film, one fleshed out with a greater attention to character backstory and more descriptive action sequences. If you are unfamiliar with the world of novelizations, your immediate reaction to their existence is likely one of incredulity. To quote my mother during a recent phone conversation we had on the subject, “People buy these books?” Yes, Mom, they do. (Apparently, she did not remember purchasing the novelization of Home Alone by Todd Strasser for me when I was a kid.) Not every novelization is a hit like Godzilla, of course, nor is it a growing part of the book industry. As studios have made bigger bets on a smaller number of films, the quantity of novelizations produced annually has decreased. But Hollywood hasn’t dropped them completely.

The novelization itself has a surprisingly long history, having popped up almost 100 years ago with silent films like Sparrows and London After Midnight. According to Films into Books: An Analytical Bibliography of Film, Novelizations, Movie and TV Tie-Ins one of the first mainstream talkies to get the book treatment was the 1933 classic King Kong. As the film industry continued to grow, publishers began producing more of these properties. By the late 1970s, studios were reaping the benefits of global franchises, including Star Wars and Aiien, both of which had novelizations that sold millions of copies. The 80s and 90s brought their fair share of tie-ins too, including everything from Howard the Duck, to Ferris Bueller’s Day Off to Batman & Robin. Today, tie-ins are mainly reserved for science-fiction and fantasy films––tent poles that translate easily into other media and come with built-in audience interest.

Novelizations may have made more sense before the advent of home video. Back then, films were released in the theater and often not heard from again. The best way to relive those original memories was to read them in book format (or to use your imagination). So, in an age of DVR and digital outlets, why do people continue to buy these books? It’s the same reason they read 5,000-word TV recaps every week. It’s a way for fans to feel more connected to a story or property they love. When you have a novelization, you get to remember at least a piece of that enthusiasm you experienced the first time around.

“People just see it as one other element of the entertainment experience,” says Katy Wild, the editorial director of Titan Publishing Group Ltd., which publishes movie novelizations, including Dawn of the Planet of the Apes and the soon-to-be-released Interstellar. “I think people who read movie novelizations are the people who go see those movies.”

Novelization authors are typically paid a flat fee in the low five-figure range to complete the work (if they’re lucky, they may get 1 to 2 percent royalties). The money, however, is only one reason writers sign up in the first place.

“I took it for two reasons,” says author Alan Dean Foster, about his decision to get into novelization writing, which has included everything from Star Wars: Episode IV to Terminator Salvation. “First, because I was a young writer and I needed to make a living. And because, as [a fan], I got to make my own director’s cut. I got to fix the science mistakes, I got to enlarge on the characters, if there was a scene I particularly liked, I got to do more of it, and I had an unlimited budget. So it was fun.”