List of inconsistencies in Halo

This list is compiled to show the various discrepancies spotted in the Halo universe. It is difficult to decide which resource is "superior" to another, so usually, the inconsistency is mentioned in the articles that it involves.

If you think you can explain an inconsistency, do so here, on the article's talk page.

There are two types of inconsistencies: Conflicts and Discrepancies. Conflicts happen when two sources disagree about a situation, subject or object. Discrepancies occur when a seemingly impossible event happens without any explanation.

Halo: The Fall of Reach

 * On page 46, Kelly handed out parts of a map to the seventy-five SPARTAN-II trainees. Then on page 48, when John checked to make sure the children arrived at the lake, he counted sixty-seven...which seemed to be supposedly all of them.
 * This discrepancy was corrected in the 2010 re-issue of the novel.
 * The London was included as a mistaken reference to the in some earlier editions.
 * A UNSC frigate was referred to as the, and then shortly thereafter as the . Fixed in 2010 re-issue.
 * The ship is referred to as a cruiser and then later as a carrier.
 * On page 19, Michael Stanforth was said to be a Vice Admiral, and on page 95, it said he was a Rear Admiral.
 * James' left arm was burnt off by a Fuel Rod Cannon, but it said in a few pages later that he saluted John-117 with his left hand.
 * This discrepancy was corrected in the 2010 re-issue of the novel.
 * In 2552, Doctor Halsey is only speculating the existence of the Elite race. Elites were encountered by humans before in the Battle of the Rubble, the First Battle of Arcadia where the Spartan Group Omega fought. They were also recognized by Kurt in a mission recording, and most importantly, the UNSC captured an Elite alive during the Battle of the Great Bear.
 * The Pillar of Autumn was missing its port-side emergency thrusters, but later used them twice.
 * Captain Keyes refers to Ensign Lovell as "Michael" instead of "William."
 * While riding to Reach Station Gamma, Kelly-087 tells John that the Spartans are "All secure." Kelly is not even in the Pelican at the time. Either the author meant to say "Linda" or Kelly spoke on through the COM.
 * During John-117's mission to Reach Station Gamma, a Jackal's blood is said to be blue although it is clearly purple. The same mistake is made with the Elites, saying that their blood is green, while it too is purple.
 * The book describes Lt. Hikowa as male, but then later refers to the lieutenant as female.
 * UNSC ships do not seem to possess artificial gravity, instead relying on rotating sections to produce gravity. However, the has artificial gravity in 2531, as do most other UNSC ships described after the book was published. (This is not an inconsistency, the vessel that lacked AG systems was a UNSC prowler class vessel, designed to be a stealth ship. The AG systems on the prowlers are seen as security threats due to the fact that they increase the ship's Electromagnetic signature, thereby making them easier to detect by enemy sensors.)
 * On page 282, after chapter 31, when the Covenant first enter Epsilon Eridani System, it states that the year is 2542, when it should be 2552. It continues this right up until the end of the book. This was obviously a typo. (reprints have date amended to 2552.)

Halo: Combat Evolved

 * The main view screen on the Pillar of Autumn label Halo by name, despite humans not knowing of its existence yet.
 * The screen could have been referring to it by its shape, though the degree of coincidence is unlikely.
 * The data Cortana had researched under Sword Base could have referred to Halo by name, although this is unlikely as well.
 * Cortana says she cannot begin to calculate the pulse range of Halo just after 343 Guilty Spark finishes telling her it has a radius of exactly 25,000 light years.
 * This may not be a mistake: she did not state she wanted to know the range, she simply stated she cannot calculate it. Since Cortana is an AI with an insatiable urge to know everything she can, she may have tried to calculate the range herself regardless of whatever 343 Guilty Spark had simply told her.
 * Almost every Pelican dropship bears the marking of Foehammer's bird, "E419," on its side, despite the fact that each Pelican has a different serial number.
 * Bungie only designed two models, V933 and E419. They used the two to represent every Pelican.
 * Pvt. Jenkins' record view on the level 343 Guilty Spark shows the date as the 27th of May 2552 when The Maw clearly takes place on September 22.
 * Frankie has confirmed that the date calibration of his equipment was not performed, causing the apparent discrepancy.
 * The pilot of John-117's lifeboat is referred to as "Lieutenant," but says "Aye aye, sir" to John-117, even though Lieutenant is a higher rank than John-117's rank.
 * This could be because nearly all UNSC personnel owe subordinate respect to the Spartans to some degree.
 * John-117 had mission command and thus commanded all survivors, since his orders came directly from Captain Keyes, the commander of the entire operation. His mission was to get Cortana off the ship (and onto Halo in an attempt to save humanity), and therefore he had tactical superiority.
 * In The Maw, the main objective is to trigger a "Wildcat destabilization" of the Pillar of Autumn's fusion reactors. Later, Cortana tells Foehammer that the engine sustained more damage than she thought because of the Wildcat destabilization.
 * This may be because the engine decay rate was faster than Cortana originally anticipated; she theorized it must have taken damage on impact. Note that the rest of the humans on Halo were aware of the plan to blow up the ship.
 * In The Maw, the player has to travel a direct distance of over 3 kilometers atop the Pillar of Autumn to reach the Longsword fighter, but the Autumn is only 1.17 kilometers long.
 * In the ending cinematic of The Maw, the Longsword fighter flies out of the side of the Autumn. The Longsword's launch bay is at the end of the Warthog run, which means that John-117 traveled from side to side. This makes even less sense than the Autumn suddenly being two kilometers longer.
 * In Halo: The Fall of Reach, Hikowa and Dowski are female officers of the Pillar of Autumn. However, on the level Pillar of Autumn, the bridge has no female members.
 * Meaning that, like modern navy ships, the Autumn must have rotating shifts.
 * The only female model (besides Cortana) in the game is the Lieutenant pilot of John-117's Bumblebee.
 * William Lovell's eyes are green, but the Autumn's crew has no green-eyed members.
 * Game designers do not generally color the iris. Instead, the game only shows the pupil. Captain Keyes is an exception, as his iris color can be seen in the opening cinematics.
 * During the level Assault on the Control Room, Staff Sergeant Johnson can be seen with John at the time he was really with Captain Keyes searching for the Covenant's "weapon cache."
 * Bungie was reusing Johnson's model instead of creating another Sergeant model.
 * In 343 Guilty Spark, when John-117 arrives at the room, he finds Pvt. Jenkins' mission recording. As he opens the door a body collapses on him. This body should have been infected by the Flood.
 * This may have been done simply to add tension and suspense to the level.
 * It may also be accounted for by the AWOL Marine's statement that the Flood only took the living ones.
 * It's also possible the body was left there as a trap to help lure in anyone who came there to investigate. This is unlikely though since no Gravemind had yet formed on the Halo; the Flood was still in the Feral state and could not make tatical plans.

Halo: The Flood

 * During a skirmish with a force of 100 Ghosts, the book describes how snipers and rocket-launcher-armed Marines could not be hit by plasma fire, as the Ghosts' weapons were fixed and the marines were on a hill. Yet in the game, the Ghost's plasma cannons can easily increase or decrease their angle. They could have easily killed the marines, unless they were positioned on an extremely tall and steep hill.
 * On page 101, it stated that "the Spartan was carrying a full combat load of ammo, grenades, and other gear, plus two magazines for the M19 launchers." John-117 was not carrying a Rocket Launcher at the time and if he was, he was never seen using it.
 * It also states that John ran out of ammo for his MA5B Assault Rifle, switching to an M6D Pistol. There are no pistols on that level at all.
 * Weapons in-game sometimes do not follow the ones written in the book, and stocks of ammo left behind by dead marines are not mentioned either.
 * On the Truth and Reconciliation chapter, it describes that a Marine was killed and, "his rocket exploded harmlessly..." No Marines were seen wielding a rocket launcher on that or on any other level.
 * Same as the above, but they do not have animations for holding a rocket launcher.
 * In the book it says that three weapons would be unwieldy for John, not to mention "damn heavy." It then says he chose a shotgun and sniper rifle. Later, an Elite sliced his sniper rifle (presumably with an Energy Sword), prompting John to draw a pistol. It was never explained how he obtained the pistol; however, its small size may have exempted it from John's personal two-weapon limit.
 * Sergeant Parker is referred to as a he, and then a she.
 * Supposedly the Second Squad was completely consumed by the Flood, specifically saying that their numbers dwindled until two PFCs remained, before the last of the Marines fell. A page later, however, Foehammer picks up the surviving Marines. This contradicts the other information, though it is possible that part of the second squad was separated, or that she did not know second squad was entirely KIA.
 * First Lieutenant Melissa McKay's mission clock is prefixed by an extra 1. It should be noted that the last time it shows her mission clock, the clock reads D+144:38:19. John-117's last mission clock mention reads D+76:18:5 while he is en route to the Pillar of Autumn. It would not take over 5 hours to detonate the ship, let alone 70 hours.
 * Sergeant Stacker is not mentioned in the novel. He is replaced during the raid on the Truth and Reconciliation by Sergeant Parker, and for the raid on the Silent Cartographer by Gunnery Sergeant Waller. One place where he might make an appearance is when John rescued a crashed Marine squad with a Sergeant and where Stacker is normally found in the game.
 * While John is on his way to the Truth and Reconciliation for the first time with his squad of marines, the Spartan runs into two jackals. He punches one and it falls off a cliff, and he shoots one with his assault rifle. Then it says a marine shoots each jackal in the head, even though there was only one jackal next to him.
 * At one point, the book states: "Consistent with his status as a veteran, the first alien to come around the corner wore red-trimmed armor, a methane rig, and a Marine's web pistol belt. The alien wore the captured gear Pancho Villa-style and dragged it across the deck. Two of his comrades brought up the rear." That is three Grunts in John-117's sight. The next paragraph says, "Confident that there were more of the vaguely simian aliens on the way, John-117 paused long enough to let more of them appear, then opened fire. The recoil compensators in his armor dampened the effect, but he could still feel the handgun kick against his palm. All three of the Grunts went down from Headshots." It is as if the extra Grunts that appeared simply disappeared. Only three Grunts were killed, which are the three original Grunts that first appeared: the leader and the two followers. But "...John-117 paused long enough to let more of them appear, then opened fire... All three of the Grunts went down from Headshots." It is possible, though, that John-117 had simply expected more Grunts to appear; he may have simply waited in case more Grunts appeared, and then opened fire when he was sure there were not any. It is also possible that John-117 was simply waiting for more of the three Grunts to appear, giving him larger target silhouettes to hit.
 * While in the Library, John comes across a dead marine that Spark explains by saying that he originally took him instead to try and find the index. The Spartan laments over the death of such a skilled trooper to have made it this far in the library, picks up his ammo, and moves on. No such marine is found in the level in game.

Halo 2

 * In the video "Another Day at the Beach," the soldiers depicted are ODSTs. During gameplay, the soldiers at the hotel are standard Marines. Also, the location of the crashed Pelican does not match its position in game.
 * This is probably because the cutscene was cut from the original game.
 * In the level Delta Halo, you can find dead ODSTs all around the level -- 7 to be exact. However, In Amber Clad only dropped 11 HEVs... 3 ODSTs, John-117, 3 more dead, and the seven ODSTs makes 14 dead soldiers. This may just be a secret 7 reference, however, as 7=7 and 7x2=14.
 * It is also possible that In Amber Clad launched more HEVs.

Halo: First Strike

 * The Longsword that landed in the Ascendant Justice is repeatedly referred to as a Pelican.
 * Vinh is referred to as Spartan-029, even though that was Joshua's tag. The mistake is probably a typo.
 * It is stated that Dr. Halsey always referred to John by name, and never by rank or serial number. But in Halo: The Fall of Reach, she called him "Master Chief" repeatedly.
 * It is stated that the ship John-117 and Cortana capture, the Ascendant Justice, is a supercarrier. If this were true, it is extremely improbable that the addition of a UNSC Frigate's power system (the Gettysburg) would make any difference in the Ascendant Justice's performance, as a supercarrier is literally 50 times the size of a frigate, with recorded lengths of 27km and 490m, respectively. It is more likely that Cortana could have opened the launch bays and fit numerous Frigates inside, which she would need to make any appreciable power source comparable to what is required to operate a supercarrier. The statement that the Ascendant Justice is a supercarrier may be the fallacy in all of this, because it is described as, "larger than any Covenant ship John-117 had seen...over three kilometers long." While this may in fact be the largest ship John-117 has ever seen, this three kilometer length is nothing compared to the 27 kilometer length attributed to supercarriers. So the fault may be in calling it a supercarrier, in which case it is most likely a destroyer or cruiser of some class. in this case, a pairing with the Gettysburg would create sufficient power for the Ascendant Justice.
 * In Chapter 12, Fred and Kelly are forced to make a hard landing after their banshees were hit by large needler shards. As they descended, an EMP washed over them, taking out their HUDs and Shields. However, they were still able to communicate over COM channels before they hit the ground.

Halo: Ghosts of Onyx

 * The date listed for chapter forty is November 4 when it should be November 3. The two chapters take place back to back, but the paperback printing puts the two events just over twenty-four hours apart.
 * The date listed for chapter forty-one is November 4 when it should be November 5. The survivors of Onyx entered the portal on November 3 at approximately 22:05. Chapter forty-one states that they had been there for a day and a half, but takes place on November 4 at 11:00.
 * In chapter thirty, Dr. Halsey shows her Spartan escort a map of their location. The map also displays Mendez and Ash on the Spirit dropship they'd arrived in. However, Kurt had assigned Dante to guard the Dropship with Mendez. Ash should have been in the room with Halsey.
 * In page 45, Captain Gibson and Rear Admiral Rich have switched ranks: instead of "Captain Gibson," the book says, "Captain Rich."

Halo 3

 * Every Longsword fighter bears the marking 7-89 on its side, despite the fact that each Longsword is supposed to have a different serial number. This is likely the result of reusing the same model.
 * In the ending cutscene of the level The Storm, all of the UNSC Frigates have the same serial number and are labeled, "Forward Unto Dawn." One of the Frigates is actually the Forward Unto Dawn. This is also likely the result of reusing the same model.

Halo Wars

 * In the level Dome of Light, after requesting the first Rhino to be deployed, the radio operator on the will identify the player as "Harvest Surface Command" even though the level takes place on Arcadia; however this could be that the Spirit of Fire was still assigned to Harvest.
 * The SPARTANs are wearing Mark IV MJOLNIR armor because the story takes place in 2531, 21 years before Reach would fall to the Covenant, however in-game they possess recharging energy shields, a feature that was added in the Mark V armor. This is only a gameplay mechanic and should not be taken as canon. The developers confirmed that the SPARTANs' shield were featured merely to enhance gameplay.
 * The Spirit of Fire is presumably equipped with a standard Magnetic Accelerator Cannon. A destroyer-class vessel can fire two rounds with one charge, as it possesses two separate MACs. The could shoot three rounds with one charge, as it possessed an advanced prototype. Super MACs around Reach and Earth could fire one round every five seconds. The MAC aboard the Spirit of Fire is able to deliver four rounds with a single charge, something that is unheard of in a shipborne MAC. However, as the rounds do very little damage to the area surrounding their targets, it may be assumed that the rounds, or the MAC itself, are not standard, or that the rounds are fired with a lower-than-normal charge.
 * Presumably, only honor guards are permitted to wield energy staves. However, in the cutscene "Monsters," in which the Spartans fight Elites while Sergeant Forge tries to activate the reactor, blue-armored Elites are equipped with energy staves. This may mean that these were honor guards composed of Elite minors, or that they were granted energy staves to fight with. It should be noted, however, that these Elites are seen uncloaking, as well as being clad in unshielded, light blue armor, perhaps suggesting that they are Stealth Elites.
 * In all renders and cutscenes, most notably "She Is Not My Girlfriend" at the beginning of the level Anders' Signal, the M41 Light Anti-Aircraft Gun is shown with four barrels. It is likely that this is either a variant of the M41 LAAG or a product of artistic license. This four-barreled design is also featured in the The Package, a short from Halo Legends.

Manual vs Books
(These discrepancies are created when material from the game manuals is inconsistent with material from the novels.)


 * The Halo: Combat Evolved Manual states that the Harvest incident took place in 2520, while all other sources specify 2525.
 * The manual also states that Captain Keyes has served in the UNSC since 2526, though he was fresh out of the UNSC OCS in 2517.
 * The Grunts are referred to as being five feet tall, but in The Fall of Reach, they are referred to as being a meter tall (a little over three feet). Although it could be that Grunts are "a meter tall" in a natural combat stance, while they are actually "five feet tall" if they stand up straight, without a Methane Tank attached to their backs.
 * If Grunts were 5 feet tall at all times, that would make the average marine around 6.5 feet tall.

Game vs Books
(These are created when the novels describe events that are not the same as what is seen in gameplay. As explained in this forum post, the games are considered by Bungie to be more canon.)


 * Quite possibly the largest discrepancy between the books and games: In the book The Fall of Reach, Dr. Halsey does not know about the Spartan III program at all until Reach has truly fallen and she has taken refuge in CASTLE base, when she hacks into ONI's database despite Colonel Ackerson's personal AI, Araqiel, attempting to stop her. In the game Halo: Reach Dr. Halsey communicates with Noble Team multiple times well before Reach is overrun, and Noble Team contains multiple Spartan IIIs. The game portrays her as having complete knowledge of the Spartan IIIs much earlier than the books.
 * Her journal shows that she did not recognize Noble team and realized they weren't "her" Spartans (aside from Jorge, of course). She still would've assumed they were Spartan-II's, there's no reason she would know of the Spartan-III's or the fact that most of Noble Team were Spartan-III's.
 * Jackals and Special Ops Elites are said to be on board the Pillar of Autumn in Halo: The Flood. This does not occur during gameplay on any difficulty.
 * They could have been on a different part of the ship.
 * The primary insertion group during the Truth and Reconciliation assault is made up of ODSTs, while in-game there are only Marines. ODST's did appear in Halo: Combat Evolved (contrary to popular belief), although they did not wear ODST Body Suits in that game. These could have been separate insertions, but a singular attack is more likely.
 * Cortana identifies Halo in Halo: The Flood when escaping the Pillar of Autumn, but it is not identified until the level The Truth and Reconciliation in the game.
 * Halo: The Flood describes only four Scorpion tanks being retrieved from the Pillar of Autumn, which does not account for the one in Assault on the Control Room. Fire Team Zulu was working out of Alpha Base, so they could have been ordered to bring the tank, which would account for it being near a downed dropship.
 * Cortana accesses Halo's Control Center by having John-117 remove the memory chip from his helmet and place it in the console, while in the novel she broadcasts herself into the system using the suit's transmitter.
 * UNSC ships use rotating sections to simulate gravity yet no such mechanism is seen in-game. This could be accounted for if the rotating parts were inside the ship. The Pillar of Autumn may also have been using the reverse-engineered Covenant technology called Gravity Plating instead of rotating sections.
 * The Pillar of Autumn's MAC cannon is depolarized and cannot fire, yet the gun is apparently used, and the loss of fire control still makes headlines in Halo: Combat Evolved's opening cutscene.
 * The cutscene in Halo: Combat Evolved at the end of the level The Pillar of Autumn clearly shows the Autumn being fired upon with plasma. However, in the novel, the Prophet at the ring forbids the Covenant ships to fire, lest they strike the "sacred relic." However, the order could have been ignored or overruled (perhaps by the Supreme Commander) to stop the Autumn from hitting the surface, as the Prophet's demand was made before the ship was even boarded.
 * Grunts often overcharge their Plasma Pistols in the books, yet they never do so in the games, with the exception of Halo: Reach and Halo 4.
 * In the game, John-117 throws Private Jenkins' Record View away, but he still has it in First Strike. This could be explained by John's suit automatically making a copy of Jenkins' recording as a possible means of gathering intelligence, although this is only a theory.
 * In the Halo Graphic Novel—specifically the Last Voyage of the Infinite Succor—the Flood are shown consuming every possible living creature they can find, yet in the games, it seems that they are only interested in intelligent beings. Additionally, the Halo Array was mentioned as only being able to kill beings with sufficient biomass and intelligence to support the Flood. However, the Flood was in its feral stage, and could have been searching for more calcium to sustain its Proto-Gravemind.
 * In the game Halo 3, under the Multiplayer Armor Permutations menu, it states that the ODST helmets were used for the Spartans to train in. However, this is never mentioned in Halo: The Fall of Reach. It may have been omitted, however, as large sections of the training are not covered in the book.
 * In Halo: The Flood, most of the Marines described in the book were female, despite no female marines being in Halo: Combat Evolved at all.
 * In Halo: The Flood, Captain Keyes comments that a single plasma torpedo is capable of destroying the Pillar of Autumn, though in Halo: Combat Evolved it is struck by several without losing structural integrity and breaking up. This possibly again relates to the Minor Prophet's order to not fire Plasma Torpedoes. The Covenant ships may have chosen to fire undercharged shots to minimize damage caused by stray shots.
 * In Halo: The Fall Of Reach, John-117 was at the edge of the system with the rest of the Spartan II's, waiting to enter slipspace with Cortana, where as in the game, John-117 is in cryosleep drydocked on Reach waiting on Noble 6 to deliver the Cortana fragment before fleeing the system, long after the Battle of Reach had begun.
 * In Halo: Glasslands, Evan Phillips says to Serin Osman concerning a sangheili diplomat, "And don't call him an Elite. Use the proper name. It matters to them." However, in Halo 2, when the Arbiter and Rtas 'Vadum are conversing in private before the raid on the Heretic facility, 'Vadum specifically says, "These are my elites- Their lives matter to me; yours does not."
 * In Halo 3: ODST during Sadie's Story, Dr. Endesha states that New Mombasa is the only place on Earth the Covenant were attacking, yet in Halo: Ghosts of Onyx, Frederic-104, William-043 and Linda-058 are fending off an incursion in Cuba.
 * However, it is possible that Cuba came under attack during the two week period between these events, or that Dr. Endesha was unaware of the attacks elsewhere.

Books vs Books
(These errors happen when information from some of the novels is inconsistent with information from other novels.)


 * 33 SPARTAN-IIs successfully adapted to the augmentations. Kurt-051, Sheila, and Randall were listed as MIA before 2552, as were Jai-006, Adriana-111, and Mike-120. Samuel-034 and three other Spartans were KIA, and one WIA, but thirty SPARTAN-IIs were present to defend Reach (John-117, Linda-058, James, and twenty-seven of Red Team). Other KIA Spartans include Cal-141, Solomon-069, and Arthur-079. Douglas-042, Jerome-092, and Alice-130 became stranded outside UNSC-controlled space, unable to contact allied forces Maria-062 was stationed at Earth, where she had plans of "starting a family." By this count no more than 19 SPARTAN-IIs, apart from Jorge-052 of Noble Team, could have been present for the Battle of Reach.
 * The Pelican's maximum operational capacity is listed as 12 Marines; elsewhere as 3 crew, 10 seated, 5 standing; yet still elsewhere they can carry 75 children, 30 Elites, or 27 Spartans. It should be noted, though, that the Pelican in Halo: First Strike has all the unnecessary equipment removed—likely including the seats—and the Spartans are more or less jam-packed into the small craft. It is most likely that there may be different variations of Pelicans, because we see 2 types of them in game, or that these were equipped with some kind of troop bay extension.
 * During the Battle of Reach, many Covenant ships are destroyed, but not before they can let loose their own lethal plasma attacks. However, later plasma en route to a target merely dissipates as the originating ship and its magnetic controls are destroyed. It is possible that the ships were destroyed when the plasma shots were very close to their targets, meaning that they hit the stations before they could completely dissipate, or the magnetic controls were not destroyed in the former instance, allowing the plasma to continue to its target.
 * The foreword of Ghosts of Onyx is an excerpt from page 249 of First Strike, discussing the 'MIA clause' of the Spartan-II Programme. In First Strike, part of the quote goes "[Dr. Halsey] touched SPARTAN-034's entry." In the Ghosts of Onyx foreword excerpt, it reads (likely due to a typing/spellcheck error) "[Dr. Halsey] touched Trover wTAN-034's entry."
 * Halo: The Fall of Reach states that Harvest has a population of 3 million. However, in Halo: Contact Harvest, it is stated to have a little over 300,000.
 * Lieutenants Hall and Dominique are introduced as members of the command crew of the Pillar of Autumn, but are absent when the ship arrives at Installation 04. It should be noted, though, that Halo: The Fall of Reach states that there was a flutter in Dominique's heart when he came out of cryosleep prior to the discovery of Alpha Halo, perhaps indicating cardiac arrest.
 * Engineers are supposedly first seen by humans during the Battle of Sigma Octanus IV in 2552. However, in Halo: Ghosts of Onyx, when Kurt is reviewing a mission of the SPARTAN-IIIs some years prior to that battle, he saw Engineers. Such information could have been kept classified by the ONI due to the secrecy of the SPARTAN-III program. Engineers are also occasionally seen in the campaign of Halo Wars, which takes place in 2531, although is supposedly MIA.
 * Chronologically, the first time Brutes are encountered by the UNSC was at the Battle of Harvest in 2525, yet John-117 has no intelligence on them until the attack on the Unyielding Hierophant in 2552. This could be accounted for by the secrecy of the first encounter with the Covenant, as the ONI could have tried to cover up the failure of the negotiations with the Brutes. Later material, such as We Are ODST, ONI Candidate Assessment Program V5.02A, The Babysitter, The Package, and multiple stories in Evolutions show that Brutes were encountered throughout the war; in addition, UNSC personnel and even civilians in Halo 3: ODST seem quite familiar with the species. Brutes are also seen during the events of Halo Wars, but only on Shield 0459, where the Spirit of Fire could not contact UNSC controlled space.
 * In Halo: First Strike, Dr. Halsey puts four sub-machine guns in a bag. In Halo: Ghosts of Onyx, Kelly found the same weapons, but they were four MA5B Assault Rifles instead.
 * The BR55 (Battle Rifle) is said to be a prototype weapon on the planet Harvest for Captain Ponder's militia in Halo: Contact Harvest. However, in Halo: First Strike, some thirty years later, it is implied that the SPARTAN-IIs saw the weapons for the first time. More recently, though, Halo Wars, The Cole Protocol, Helljumpers, and Evolutions indicate that the BR55 was in service for the duration of the war.
 * Jai remembers being abducted and brought to Reach along with seventy-five other children, when there should have only been seventy-four other children. This is probably just a typo though.
 * Prior to 2525, UNSC ships used rotating sections to simulate gravity, and the Spartan-II's were surprised to discover artificial gravity on the Covenant ship they boarded. However, since then, multiple human facilities and ships are shown to have artificial gravity capability. It is possible that this technology was adapted from the Covenant, but that is unlikely due to the difficulty in capturing intact Covenant ships, much less reverse-engineering them. The most likely possibility is that the writers used anti-gravity technology for convenience purposes. It is also possible, though, that the rotating sections exist between the walls and outer hulls of UNSC vessels.
 * The Covenant has had knowledge on the Oracles for a long time, but in Halo: The Flood, 343 Guilty Spark was regarded as an enemy to the Sangheili.
 * When Lieutenant Keyes is warned of the incoming Covenant fleet and asks what UNSC ships are nearby in Halo: The Cole Protocol, the book first states that three destroyers are picketing, but immediately counters that the and three frigates wouldn't be able to repel a Covenant assault. However, they are later confirmed to be destroyers, one of which is the.
 * Chief Petty Officer Mendez remarks that some of the Alpha Company candidates were orphaned at Jericho VII. His speech takes place on December 12, 2531, yet Jericho VII was not glassed until February 2535.
 * In Halo Wars: Genesis, Ellen Anders mentions the planet Onyx in passing, while giving a talk about an alien presence. However, in Halo: Ghosts of Onyx, Kurt reads a file that says Onyx has been classified since 2511. Genesis takes place in the spring of 2531.
 * In Halo: The Flood, it is stated that lowering ones eyes is a sign of respect among the Sangheili. However, in Halo: The Cole Protocol, it was said that refusing to meet one's eyes or lowering the head was a sign of shame.
 * In Halo: The Flood it says Captain Keyes killed his first human with a pistol; however, Halo: The Cole Protocol states he used a plasma rifle.
 * The Halo: Evolutions story, The Impossible Life and the Possible Death of Preston J. Cole, it is clearly stated that Preston Cole had one hundred seventeen ships under his command during the Battle of Alpha Aurigae. Halo Wars: Genesis states he only had one hundred seven in the same battle.
 * In various books the Magnetic Accelerator Cannon is also referred to as the Mass Accelerator Cannon. This is most likely a typo.

Game vs Game
(This occurs when information from one game is not consistent with information from another.)
 * In Halo: Combat Evolved, John-117 needs to insert a chip into the back of his helmet to house Cortana in his Mark V MJOLNIR armor. In Halo 2, with the upgrade to Mark VI, all he needs to do is touch something to allow her to move from his suit to another device. It is reverted to the chip in Halo 3, gaining some of the properties of the touch ability seen in Halo 2.
 * It is possible that not all devices that Cortana can interact with are compatible with touch transfer.
 * In Halo: Combat Evolved, the Sniper Rifle had night vision, but it is absent from Halo 2 and Halo 3. This is likely due to its limited purposes, but it is still strange to see a weapon losing an advantage, and the different versions of the Sniper Rifles during the era could not be accounted for that loss.
 * In The Flood, The Fall of Reach and First Strike, it is revealed that Spartan IIs have the ability to see very well in the dark and the Mark VI helmet automatically adjusts to light changes. The Sniper Rifle may have night vision, but as John-117 can see in the dark naturally he would not need to use night vision, therefore making it pointless to add it in the game.
 * In addition, the Rocket launcher went from having no lock-on in Halo: Combat Evolved, to possessing the lock-on in Halo 2, only for it to revert to the non-locking version in Halo 3. This was likely changed for gameplay balancing.
 * The doors in High Charity are different in Halo 2 and Halo 3. This could be because the High Charity part of Halo 2 takes place near the Prophets' Sanctum, and in Halo 3 near the core area, accounting for the difference in design.
 * In Halo 3: ODST, Solemn Penance is seen as being stationary just prior to it jumping into slipspace, yet in Halo 2 during the closing cutscene of the level Metropolis the carrier is moving forwards.
 * From the same scene in ODST, In Amber Clad can be seen approaching the carrier and is clearly separate when they jump, but in Halo 2, the In Amber Clad flies to a position underneath the starboard side of the carrier, where it would hardly be visible (if at all) to the ODSTs above.
 * In the end of Halo 3, when John-117 enters cryosleep, the pedestal in which Cortana is standing on is at the right of the cryotube John was in. However, in Halo 4, that same pedestal is now on the left of the cryotube John was in.
 * In Halo 4, The UNSC Forward Unto Dawn features the redesigned UNSC logo despite that the ship was built before the events of Halo 4. The outer hull's back still possesses the old UNSC logo though.
 * Cortana states in the opening cutscene to Halo: Combat Evolved's level Two Betrayals that Halo doesn't kill the Flood but that it kills their food, but in Halo 3, John-117 uses a 'tactical pulse' Installation 04B to wipe out all the Flood in the vicinity of the replacement Halo and the Ark and additionally, in one of the terminals in Halo: Combat Evolved Anniversary, specifically the one on Two Betrayals, it shows a Carrier Form, Tank Form and a large amount of Flood Biomass being destroyed by the firing of a Halo installatopn.
 * It is possible that Cortana was exaggerating or that the rings have multiple firing modes.

Books vs Movie

 * In Halo: The Fall of Reach, during the Battle of Sigma Octanus IV, the Spartans, including Master Chief, appear to have never encountered a Hunter before, yet Master Chief took down two of them personally in Halo 4: Forward Unto Dawn, which takes place several years before Sigma Octanus IV.

Games vs Movie

 * In Halo 4: Forward Unto Dawn, Commander Lasky is depicted as being given the choice as to whether to follow Cortana's beacon, whereas in Halo 4, Captain Andrew Del Rio was in command of the UNSC Infinity and so would have had the choice. It is possible, but unlikely, that Del Rio gave the choice to Lasky.