Though nearly every novel is connected to history in some form, not every novel could be considered historical. The two types of historical novels are those in which the author places a fictional character into a realistic and recognizable place or writes a fictional story from the perspective of a real character. Some novels do both, as in Esther Forbes young adult novel Johnny Tremain. Sansom's novels are historical.
Unfortunately, categorizing a work of fiction as crime, thriller, detective, or mystery genres is much more difficult. Those who create an official set of guidelines for a genre are generally trying to be restrictive rather than inclusive. The best indicator of a writer's or novel's genre, then, seems to come the people who do it for a living. Here is an annotated look at a few for Sansom:
- Barnes and Noble - Fiction, Mystery and Crime
- Goodreads - Historical Fiction, Mystery and Thrillers
- Online biography - "writer of crime novels"
- His own website - "master of the historical thriller."
The consensus seems to be that C.J. Sansom is the author of historical thrillers.