The Key is an Achievement for Halo 3 and Halo: The Master Chief Collection.

It is obtained when the player finishes the campaign mission "Cortana" on Normal, Heroic, or Legendary difficulty. In Halo: The Master Chief Collection, it is possible to get this achievement on Easy.

The Halo 3 achievement gives 40 Gamerpoints to the player and is represented by a blue plate with a Roman numeral VIII on it.


  • It's name is a reference to Cortana having the Key to activate the new Halo.


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