Fall of Reach
From Halopedia, the Halo wiki
The first book in the Halo series is called The Fall of Reach. The Fall of Reach details the origins of the Spartan program and also covers the beginning of the war with the Covenant leading all the way up to the discovery of the first Halo. I particularly like the parts of the book that deal with the training and special abilities of the Spartans and their place as the best soldiers in the human military. Master Chief isn’t the only Spartan, by the way. If you have ever read Robert A. Heinlein’s Starship Troopers, The Fall of Reach is told in a very similar manner which is a good thing. The title, The Fall of Reach, references a human controlled world called Reach that is a major staging area for the military. The Covenant discover the location of Reach and the resulting chaos leads to a random slipspace (basically hyperspace or light speed in other sci-fi universes) jump where Captain Keys, Master Chief, and the rest of the crew of the ship Pillar of Autumn discover Halo.