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 Marine Corps force.

Description
In Halo: Combat Evolved and Halo 3, the player plays as the Master Chief Petty Officer John-117, a SPARTAN-II. 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 of Covenant society. In Halo 3: ODST, the player plays as a variety of Orbital Drop Shock Troopers. In Halo: Reach, the player takes the role of Noble Six, a SPARTAN-III whose name, gender, and past are unknown.

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, etc. 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 2, Halo 3, and Halo Wars also have a unique, unofficial difficulty known to fans: Mythic, which is Legendary with all Skulls activated. A form of Mythic also appears in Halo 3: ODST's Firefight mode, if the player plays on Legendary and progresses far enough that all of the Skulls are activated. Halo: Reach will likely have this difficulty as well.
 * 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 unknown at this time.
 * Halo: Combat Evolved starts with Master Chief leaving a cryo 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 a huge Forerunner structure exploding: Halo: Combat Evolved ends with Halo Installation 04 exploding, Halo 3 ends with Halo Installation 04B exploding (taking the Ark with it), and Halo Wars ends with a Shield World exploding.