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Real World events
- February 26: Halo Wars is released in Japan and Australia.
- February 27: Halo Wars is released in the PAL Region.
- March 3: Halo Wars is released in North America.
- April 9: The first Mythic Map Pack is released.
- Between April 9 and July 21: Halo Wars releases a Game Expansion, along with Reinforcements, Tug of War and Keep Away.
- July 21: Historic Battles, the first map pack for Halo Wars, is released.
- July 22: Issue 1 of the Halo: Helljumper series of comics is released.
- July 24: The Announcement Trailer for Halo Legends is released.
- August 26: Issue 2 of Halo: Helljumper is released.
- September 22: Halo 3: ODST, along with a copy of all Halo 3 map packs, is released. Along with the second Mythic Map Pack.
- September 23: Issue 3 of Halo: Helljumper is released.
- October 13: The Halo Encyclopedia is released.
- October 28: Issue 4 of Halo: Helljumper is released.
- November 5: Halo Waypoint is released.
- November 7: The Babysitter short film shown on Halo Waypoint.
- November 21: The Duel short film is shown on Halo Waypoint.
- November 24: Halo: Evolutions is released.
- November 25: Issue 5 of Halo: Helljumper is released.
- December 5: The Package Part One short film is shown on Halo Waypoint.
- December 12:
- The Package Part Two is shown on Halo Waypoint.
- Halo: Reach Video Games Awards Trailer is aired live on the Spike TV Video Game Awards 2009.
- December 23: Issue 1 of the Halo: Blood Line comic series is released.