- The Halo series contains several shout-outs to one of Bungie's previous titles, Marathon, although some of these seem to be more a case of recycling phrases because they sound cool. Halo has MJOLNIR Mark VI battlesuits while Marathon has Mjolnir Mark IV cyborgs. Halo has Marathon-class cruisers. The Marathon Mission's crest has made its way into the Halo universe in several places, sometimes as canon and often as easter eggs — on the side of a ship, a robot's eye, and as an ancient alien race's symbol for humanity.
- Not to mention that the last task the Master Chief has to complete in the first game is literally to frag-blast a vent core.
- Halo 3 has a number of cameos from Sci-fi television, including "Sergeant Reynolds" (voiced by Nathan Fillion, who at one point gets to deliver the beginning of the quote on Big Damn Heroes) and a Marine voiced by Adam Baldwin shouting "Say hello to Vera!", along with Alan Tudyk delivering a very Wash-like speech "Tank beats everything". Katee Sakhoff appears from Battlestar Galactica to lend a voice to some of the female marines.
- Everyone at Bungie must love Firefly because the ODST expansion has Buck, voiced by Fillion, Dutch voice by Baldwin and Mickey voiced by Tudyk. Also characters will say 'Gorram that hurts' if shot enough. Another hilarious shout out is playing as Buck in firefight when throwing grenades he will sometimes shout, "This Is SPARTAA" He's also an unlockable voice in Reach's "Firefight" gametype; he'll exclaim "Shiny" when equipping a power weapon.
- The principal actors of the Halo inspired machinima Red vs. Blue also appear, delivering an in-character exchange, the participants and contents of which vary by difficulty level.
- One level has a section entitled "Actually, HAL, I Can Do That", a reference to 2001: A Space Odyssey.
- The first game has several Alien references:
- Sgt. Avery Johnson's appearance and personality were explicitly based on Sgt. Apone's. He even wears a cap instead of a helmet.
- The calico cat Jonesy.
- "I have a bad feeling about this (drop)"
- "We're screwed, we're screwed man!"("We're fucked, we're totally fucked!", which got changed to "screwed" in the TV version), and of course, "Game over man, game over!"
- The UNSC's uniforms and armor in the first game are based on those of the Colonial Marines.
- Most obviously, it's hard to look at anything Flood related and not think of the Xenomorphs. See the relevant entry under Xenomorph Xerox.
- The Elite species draw a lot of inspiration from the Yautjas of Predator fame. Both are 7+ foot tall superhuman proud warrior races who utilize invisibility tech and plasma guns while hunting humans, and both place such emphasis on honor and pride that it's ultimately easy for the human protagonists to outwit them. Both also come into conflict with their versions of the above-mentioned similar antagonists, the Flood and the Xenomorphs, and ultimately end up in an Enemy Mine situation with the human protagonists later in their respective franchises.
- The Master Chief is Spartan John-117. The protagonist of Demolition Man is John Spartan, Prisoner #117. Go figure.
- The protagonist of Halo: Reach is designated "Noble Six", a reference to Alfred Tennyson's "The Charge of the Light Brigade", which refers to the titular brigade as the "Noble six hundred". It's also Foreshadowing, of course.
- In Halo Wars you get control of 3 Spartans of Red Team. Their names are Jerome-092, Alice-130 and Douglas-042.
- Halo's Wolverine rocket-launching tank is basically the same as the Wolverine from G.I. Joe.
- Halo Anniversary gives us the Bandana Skull that gives you infinite ammo. Just like the bandana from another series.
- There's no doubt that Halo owes a lot to Starship Troopers, what with it being about armored humans fighting aliens, but the ODST drop pods just confirm it—that's exactly how the Mobile Infantry deploys in the novel version of Troopers.
- In a Shout-Out to the series, Microsoft named their voice assistant app in Windows Phone 8.1 and Windows 10 after Cortana. Originally it was just a codename during 8.1's development, but after word got out, fans campaigned for it to be kept. Not only did they do just that, they brought in Jen Taylor to provide the voice.
- In Halo Wars 2, the achievement unlocked by winning three games as Sergeant Forge is called "Heroes Never Die"
- One of the stories in the Halo: Fractures short story anthology features a shout-out to the hosts of the YouTube channel Outside Xbox.
- The Mantis Mini-Mecha in Halo 4 is an obvious reference to the titular Metal Gear. On entering the vehicle, the OST will change to synth-like music straight out of Metal Gear Solid.
Shout Out / Halo