From Halopedia, the Halo wiki
 Halo Universe Events
- Main article: Iris
- June 19: AdjutantReflex is taken over by another entity.
- August: Dr. Jonas Volman, the author of The Castaway Theory, returns from his absence, having gone missing in November 2005.
 Real World Events
- May 11: The Halo 3 Beta is first released to a limited audience.
- May 16: The Halo 3 Beta becomes accessible to the public.
- May 31: Halo 2 Vista is released for the PC.
- June 10: The Halo 3 Beta comes to a close.
- July 10:
- August 1: Marathon 2: Durandal is released on Xbox Live Arcade.
- August 10: An internal build of Halo 3 titled Halo 3 Epsilon is released to Microsoft employees.
- August 22: The first issue of the Halo: Uprising series of comics is released.
- August 28: Halo: Combat, the second part of the Halo: Landfall series, is released.
- August 29:
- Halo 3 goes gold.
- Halo 3 Epsilon is closed.
- September 24: Halo: Last One Standing, the final part of Halo: Landfall, is released.
- September 25: Halo 3 released in North America.
- September 26: Halo 3 released in Europe.
- September 27: Halo 3 released in Japan and the rest of Asia.
- September 28: Halo 3 released in most South Korean video game shops.
- October 30: The novel Halo: Contact Harvest is released.
- November 20: The Halo 3: Original Soundtrack is released.
- November 21: The second issue of Halo: Uprising is released.
- December 11: The Heroic Map Pack for Halo 3 is released.