At the time of Halo, humans have founded a modest interstellar empire. There are at least a few dozen, but more likely one or two hundred, colony worlds within human-explored space. Some of them, if not most, are relatively heavily populated, suggesting that these colonies have been around for quite some time.

Human technology is not that far advanced from what we have today; the basic technologies are mostly the same, just on a much larger scale, with the exception of the FTL drives of human starships. Weaponry is still projectile-based, and explosives still seem to involve chemical reactions rather than a release of contained plasma, as the Covenant explosives use. While humans seem to possess artificial gravity (as demonstrated by the gravity on the Pillar of Autumn), they do not use it on smaller planet-bound vehicles; the Warthog, for example, still uses wheels and does not hover.

The bulk of humanity still does not know about the events which transpired after the Pillar of Autumn jumped away from the Reach system; the Master Chief is the only remaining witness of our race to the Flood and the Forerunner machines left on Halo. All they know is that their last hope, Reach and her military forces, is either completely lost or severely impeded (depending on the number of surviving Spartans), and that the Covenant still loom over them. Earth cannot last long, especially after the fall of Reach.