Speedrun

A speedrun is an attempt by players to finish any campaign level as fast as possible. This is done by having good understanding of the game's gameplay mechanics and exploiting these mechanics. Common methods in a Halo speedrun is by using explosive jumping technique, careful selection of weapons and bypassing as many engagements as possible, sometimes getting outside the map to do so. Allies may also be killed to skip dialogue. Halo speedruns are typically run on either Easy or Legendary, with each difficulty being a separate category. A subcategory under Legendary, L.A.S.O. (Legendary All Skulls On) requires the runner to activate all skulls while playing on Legendary. L.A.S.O. typically requires different routing than that of a no skulls Legendary run.

Terms

 *  "Full Game" or "Marathon"  refers to playing the entire campaign in one sitting.
 *  "IL"  stands for "Individual level", and typically grinded for a better time in preparedness for a marathon run.
 *  Segmented  runs are multiple speedruns that are edited to where only the best clips are shown. A segmented run is the quickest theoretical time.

Halo: Combat Evolved
Legendary Record as of Dec 2018

Due to the performance difference between mouse/keyboard and controllers, most runners prefer to use Halo PC/Custom Edition (though Anniversary and MCC may be used if the former are not available).

Halo

 * 1) During the initial fight around the Forerunner spire, killing all the Marines despawns the fourth dropship.
 * 2) In the Forerunner cave, by jumping out of your Warthog before the wall on the right side before the bridge, the cutscene of the lightbridge appearing is skipped.
 * 3) On Legendary, most of the Marines in two of the three final areas are killed by the player from afar, leaving the other Marines to die by the Covenant.

Truth and Reconciliation

 * 1) By performing a triple grenade jump, the player can skip a portion of the hanger fight. Subsequently, this also skips a trigger allowing the level to end early.

The Silent Cartographer

 * 1) After landing, walk in the opposite direction of the Covenant forces towards the entrance to the Security Checkpoint. Grab the Warthog and continue to the Cartographer.
 * 2) By driving the Warthog into the Cartographer facility and "flinging" your Warthog and exiting, it is possible to fly through the door as the Elite closes it, negating the need to go to the Security facility (make sure to kill the Elite after you're through).
 * 3) By jumping while going into the Map cutscene, the scene can be skipped.
 * 4) Another grenade jump can be done to skip going back up most of the levels.

Assault on the Control Room
There are two variations to skip the level:
 * Drop down onto the cliff below the first bridge and precariously drop from cliff to cliff until you can safely drop down.
 * Lure a Banshee over to the entrance to the first bridge and force the occupant out. Enter the Banshee and continue.

The Library
By using a trick called "flood bumping", it is possible to skip many of the doors that normally would require waiting for up to 90 seconds.

Two Betrayals
Through a bit of wiggling, it is possible to get a Ghost or Banshee past the destroyed door.

Keyes
Using another flood bump, most of the level, including not having to go down onto the surface and back up, is skipped.

Halo 2

 * Legendary Record for H2 Classic as of Dec 2018
 * Legendary Record for H2 MCC as of Dec 2018

A major trick, known as sword flying, depends on the original Halo 2 version 1.0 and the game running at 30fps. Therefore, Halo 2 Anniversary is considered a different category.

Outskirts
By using a grenade jump, the player can reach out of bounds and walk on the roofs on many buildings, skipping the first part of the level.

Halo 3
Legendary Record as of Dec 2018

Halo 3: ODST
Legendary Record as of Dec 2018

Halo Reach
Legendary Record as of Dec 2018

Halo 4
Legendary Deathless Record as of Dec 2018

Halo 5: Guardians
Legendary Record as of Dec 2018