Halo may be best known for its games, but most of the Halo lore is actually in the books, with over forty full-length novels and short stories.
THE BUNGIE ERA
These are the books that started it all. Eric Nylund was the primary author during this period, though other authors such as Joseph Staten and Tobias Buckell got their start during this time too.
THE FORERUNNER TRILOGY
To kick off the transfer of power from Bungie to 343 Industries, two trilogies were commissioned. The first, by Greg Bear, focused on the time of the Forerunners.
THE KILO-FIVE TRILOGY
In concert with the Forerunner Trilogy, a series of novels focused on the post-war era, known as the Kilo-Five Trilogy by Karen Traviss.
THE 343 ERA
After 343 Industries took the reins of the Halo franchise, the number of novels produced increased dramatically. They generally focus on the post-war era, though they have expanded the universe from the beginnings of the Covenant to beyond the events of Halo 5.