In the show, novelist Richard Castle writes a book called Heat Wave; ABC and Hyperion Books actually published it as a real novel credited to 'Richard Castle,' complete with an in-character dedication and acknowledgments naming the cast and creators by first name.

The tie-in novel Heat Wave debuted at No. 26 on The New York Times Best Seller list and climbed to No. 6 by its fourth week; its sequel Heat Rises later debuted at No. 1.

Real-life crime writers Stephen J. Cannell, James Patterson, Dennis Lehane, and Michael Connelly appeared as themselves in recurring poker-game scenes at Castle's apartment.

After author Stephen J. Cannell died on September 30, 2010, the show kept an empty chair at the poker table for a year as a tribute to him.

Seamus Dever, who plays Detective Kevin Ryan, is married in real life to Juliana Dever, who plays Ryan's on-screen wife Jenny.

Despite several cast members signing one-year contracts for a potential ninth season, ABC announced on May 12, 2016, that the show was canceled instead, with the finale airing just days later on May 16, 2016.

In August 2014, ABC began early development on a spin-off TV series centered on Castle's fictional character Derrick Storm, to be written by Gregory Poirier and executive-produced with Andrew Marlowe and Terri Miller, but the project was never pursued further.

The Nikki Heat novel franchise continued even after the series' cancellation, with additional books like High Heat (2016), Heat Storm (2017), and Crashing Heat (2019) being published years after the show ended.