UPDATE: The below was written early in 2007. In mid-2007, Bungie announced the official release date of Halo 3 as September 25, 2007 for the Americas.

All Bungie has said so far is "2007". Speculation is already beginning that this is a conservative estimate and that Halo 3 will ship this winter. This is most likely naught but wishful thinking.

If Halo 3 were to ship in November of 2007, that would mean that Halo 2 and Halo 3 both nominally took three years. Given that this is two years or so into the life cycle of the Xbox 360, one imagines that Microsoft would not want the console's "killer app" to ship much later than this, so I think this is a very conservative guess.

If one takes Bungie's announcement at face value, one may assume that the "2007" date means that Bungie does not expect or intend to launch by the holiday 2006 season. Once the pressure to do that is off, there would seem to be little reason not to take a little extra time for polish; so it seems reasonable to assume that a launch as early as Q1 of 2007 (January through March) would make little sense.

A broad window between April and November of 2007 thus seems most likely.

If Bungie is able to avoid a change in creative direction in mid-project, perhaps the release date would be early in that window.

However, for the second consecutive sequel Bungie is not merely developing new content, but also new technology. Halo 2 was almost completely rewritten, as well as adding new middleware for physics with the Havok engine. Given that the Xbox 360 uses a different, multicore CPU and a GPU from a different vendor, and Microsoft is pushing for 720p as a minimum resolution, it seems logical to assume that Halo 3's graphics engine will probably contain relatively little legacy code from Halo 2.

How much pressure is put on Bungie to launch early in 2007 as opposed to late may very well depend on how well Sony's PlayStation 3 console performs after its launch late in 2006. If the console struggles, has availability problems similar to the Xbox 360's because of manufacturing issues or Sony's unfamiliarity with a global launch, then Bungie may be free to wait.

If Sony's global launch comes off more smoothly than Microsoft's; if there are no manufacturing issues that restrict availability; if sales are brisk and by early 2006 Sony is threatening to overtake Microsoft in next-generation console sales, then it seems likely that Bungie will be pressured to release Halo 3 sooner rather than later.

Source: Bungie Halo 3 trailer FAQ