What is the name of the Halo novel published first, in 2001?

Halo: The Fall of Reach was the first published Halo novel, released in 2001.

Written by Eric Nylund, the novel serves as a prequel to Halo: Combat Evolved. It describes John-117’s childhood recruitment into the Spartan-II program, the training and formation of the Spartans, and the Covenant attack that threatens the human world Reach. The story leads directly into the opening situation of the first game.

The book was published before Halo: Combat Evolved and helped establish background details that the game only hinted at. It is part of the expanded Halo universe, alongside later novels, comics and other media. Halo: The Flood, also written by Nylund, was published in 2003 and novelizes events from the first game, while Halo: First Strike followed in 2003 as an original continuation.