Campaign

Campaign Mode is the single player gaming aspect of Halo: Combat Evolved, Halo 2, Halo 3, Halo 3: ODST and Halo: Reach, where the player takes control of a single character at a time through the canonical storyline of the Halo trilogy, and the single player aspect of Halo Wars, where the player takes control of an entire UNSC Army force.

Description
In Halo: Combat Evolved and Halo 3 the player plays as John-117, in Halo 2 the player plays as both Master Chief and the Arbiter Thel 'Vadam a Covenant Elite, which allows the player a more personal view on Covenant society. In Halo: Reach, the player takes the role of Noble Six, a nameless and genderless SPARTAN-III attempting to defend the falling planet, Reach.

In Halo Wars, the campaign has a different gaming aspect. The game is a strategy video game, and the player takes control of a whole base, troops and vehicles. It is up to him to decide where a squad will go, when a building will be constructed e.g. Again, the game follows the canonical storyline of the Halo Universe.

The Campaign Mode can be played on four difficulty levels, listed in order from most difficult to the easiest: Legendary, Heroic, Normal, and Easy. In addition, Halo: Combat Evolved and Halo 2 have a co-op Campaign option permitting two players to play through campaign either in split-screen or via system link between two Xbox gaming consoles. For Halo 3, the number of players permitted has changed to allow up to four players and the use of Xbox Live.

Trivia

 * Halo 3 also has a unique, unofficial difficulty known to fans. One of them is Mythic, Legendary with all Skulls activated.
 * Every Halo game starts and ends with the player in space. In Halo:Combat Evolved, the game starts with Master Chief on the Pillar of Autumn and ends with him in a Longsword. Halo 2 starts with him on Cairo Station and ends with him on the Forerunner Dreadnought. Halo 3 starts off with him crashing towards Earth and ends with him stranded inside the . Halo 3: ODST starts with The Rookie on the and ends with him on an ONI orbital facility. Halo wars starts with Captain Cutter on the  talking about the war on Harvest and ends with the freezing of Professor Anders. Halo: Reach could be an exception but this is yet unknown.
 * Halo: Combat Evolved starts with Master Chief leaving a cry pod and Halo 3 ends with him entering one again.
 * In Halo: Combat Evolved, Halo 3 and Halo Wars, the endings of the three games end with an exploding Forerunner structure: Halo: Combat Evolved ends with Halo Installation 04 exploding, Halo 3 ends with Halo Installation 04B exploding, and Halo Wars ends with a Shield World exploding.