After Halo Reach ended, there were several books that came out to setup Halo 4

> Forerunner Saga
Greg Bear wrote three books about the forerunners, humans and their final fight with the flood. The book demystified the forerunners and made them distinguished.
>Kilo 5 Trilogy
Karen Traviss wrote 3 books about the post-war humans and their attempt at regaining a foothold after the fall of the covenant.

Halo 4 and 5 attempted to take lore of both these books and establish them into the game, and did not do a very good job at it. Karen Traviss ruined post-Halo 3 and Ghosts of Onyx lore.

>Greg Bear: Cryptum, the first Halo novel, and so anyone who’s a Halo fan is going to enjoy the collaboration between the people in [Microsoft’s] 343 [division]—Frank O’Connor and Kevin Grace

>Frankie: I was always doing little tiny incremental things with development throughout, but where I really started working on things going directly into the game was Halo 3, when I worked with (engineer) Damian Isla on the terminals that explained the deeper lore. So I was doing more and more story as we got towards the end of it, and as we started Reach, I got the chance to actually write the script.

>Frankie: Most of the books for the last two years have dealt with building backstory for Halo 4, rather than fixing canonical errors or mismatches. We've bought ourselves a little bit of latitude with the terminals in previous Halo games. We knew that the fiction was going to evolve when we were writing the terminals for Halo 3.

>“Every novel that you’ve read in the last couple of years, every comic book, the Terminals in Halo Anniversary […] everything is feeding directly into the story for the next Halo trilogy.” [Frank O’Connor, Halo Fest 2011 – Halo 4 Panel (2:50)]

>Halo TV is obviously Frankie's child. This show is what he always wanted Halo to be, outside of the Forerunner stuff. A generic Expanse rip-off with Spartans and feminism