Because lots of movies and TV shows these days benefit from the additional storytelling avenues (not to mention the cash) that comes from tie-in books and comics runs, they've become increasingly popular. The latest series announcing spin-offs is Star Trek: Picard.
Picking up years after the events of Star Trek: The Next Generation and the various movie outings of the crew, it'll find Patrick Stewart's Jean-Luc Picard retired from Starfleet and spending time on his family vineyard, but called back to adventure by a dangerous new mystery.
IDW Publishing has Star Trek: Picard – Countdown, a three-issue series written by Mike Johnson and Picard co-writer Kristen Beyer, focusing on a single mission that changed the character's life forever. That'll run from this November to January next year. Then Galley Books will publish Una McCormack's The Last Best Hope, which will lead directly into the new show and introduce some of the other characters.
The series itself (which launched a new trailer at San Diego Comic-Con a couple of weeks ago) arrives in the States via CBS All Access early next year. UK audiences will be able to catch it on Amazon Prime around the same time. And yes, this writer pre-apologises to Empire editor Terri White and Pilot TV podcast co-host Boyd Hilton for the potential can of James-splaining this might open up.