Long before it was a popular TV show, Robert Kirkman’s zombie saga, the Walking Dead, was a hit comic book series, first published by indie comics publisher Image Comics in 2003. The show’s seventh season recently started on AMC; the bestselling series is now published in book collections by Skybound, an Image Comics imprint launched in 2010 under the direction of Kirkman; and sales continue to rise.

Skybound editorial director Sean Mackiewicz said that Walking Dead hardcover and trade paperback collections have sold more than 289,000 copies in 2016 through September, an increase of 12% over the same period in 2015. He added, “If we were to include tie-in publications, such as coloring books, the total Walking Dead franchise sales would be up 18% year to date in 2016.” In a 2011 interview, Kirkman told PW that the Walking Dead graphic novel collections, of which there were 13 at the time, had first printings of 100,000 copies per volume. These days, Mackiewicz said, initial printings are around 300,000 copies. The most recent Walking Dead trade paperback release, No Turning Back, the 25th volume in the series, has sold 40% more copies during its first 13 weeks than the previous volume sold over the same period, he noted.

“Skybound was launched as an imprint to bring in new artists under a new platform,” Mackiewicz said. It publishes about eight comics series annually, including several by Kirkman. All of them, Mackiewicz noted, are gathered into trade paperback collections. Skybound’s book list is distributed to the trade by Diamond Books Distributors and its titles are available digitally on Comixology and elsewhere.

After the Walking Dead, Skybound’s bestselling book series are Outcast, a horror series by Kirkman and artist Paul Azaceta; Invincible, a superhero series by Kirkman and artists Cory Walker and Ryan Ottley; and Manifest Destiny, a paranormal frontier adventure by Chris Dingess and artist Matthew Robert.

The Walking Dead series also includes the Walking Dead Compendium, massive trade paperbacks priced at $60 that each include eight trade paperback collections and sells thousands of copies annually. There are now three compendium volumes, which are collected and published every four years. Mackiewicz said that the compendiums have been “huge for us,” attracting “a stream of consumers who are... filtering into the standard trade collections to keep current on the story.”

The Outcast series has also been adapted into a TV show that just completed its first season on Cinemax and Fox. Sales of Outcast, Vol. 1, which was published in January 2015, are up 46% this year through September over the same period last year. Skybound has released three trade paperback volumes of the Outcast series (with volume four coming in 2017) and is about to release a deluxe hardcover edition in November.

“We’re quickly establishing an Outcast footprint on retailers’ shelves,” Mackiewicz said. “As we get deeper into the publication of the [Outcast] series and more volumes are introduced, we see a consistent strength [in sales growth] on our early volumes alongside the new releases. Books are where comics consumers are going, and the book market is a huge focus for us going forward.”

Correction: Skybound publishes eight comics series annually (the number was wrong in an earlier verison of this story) and the names of the artists working on the Invincible series were also incorrect in the earlier version.