The Codex is the constitution and set of laws for the Brotherhood of Steel.
Written and managed by the Scribes, the Codex acts as the building blocks and the very definition of the Brotherhood, and is a documentation of the entirety of its history, listing every piece of information relating to the organization, such as their doctrine, ranks and their responsibilities, members, tactics, and much more. The personal principles and idealism of Roger Maxson are also contained within.
The Scrolls are an important area of the Codex, and cover the lives and deeds of all Brothers, and its upkeep is the duty of the head librarian of each Brotherhood installation. The information held in the Scrolls can be a member's biography, contributions, the battles they partook in, kills, promotions, technological discoveries, and their death to name a few.
The Oath, or the Oath of Fraternity, is a Brother's/Sister's signing of agreement to brotherhood/fraternity and with the Codex's teachings. In the Capital Wasteland Brotherhood, due to the chaotic situation with the Brotherhood-Enclave War and the Capital Wasteland super mutant conflict, many initiates were pressed into service before taking the Oath.
- In Fallout 3 the Brotherhood Outcasts have been struck from the Codex for defying Elder Lyons' orders and disowning their East Coast brethren in order to return to their original mission of securing technology.
- Both Arthur Maxson and Star Paladin Cross from Fallout 3 recite excerpts from the Codex.
- In Fallout: New Vegas, if the player character has the Terrifying Presence perk while doing the quest I Could Make You Care, they have the option of using the dialogue "I will cast down your Codex and bask in the dying agony of those who hold it dear." which will in turn scare away the Brotherhood of Steel who are tracking down Veronica.
- Because the Mojave Wasteland branch remains true to the original Brotherhood of Steel Codex, it uses the traditional ranking system where the Paladins serve as a separate soldier caste, unlike the Capital Wasteland branch where both Paladins and Knights fight battles.
- "He may have struck our names from the great Codex, but we'll be vindicated in the end, and our names will be restored." – Henry Casdin
- "Scrolls are kept by the Head Librarian of each Brotherhood bunker. The Scrolls are a record of the Brotherhood itself. Into each Scroll is written the name and deeds of each of our Brothers. Battles, what technology he has recovered, when he was promoted. Everything. The last entry for each Brother is that Brother's death. It is important, as the way a man dies is just as important as the manner in which he lives. And so each man who nobly serves the Brotherhood ascends into our history, to be remembered by those who come after him." – Scribe Jameson
- "Ah, the Codex. If it's in there, we have to abide it, if it's not, it's not important. It documents our history, too. Part of what Scribes like me do is update it. Hmm... I wonder... Nah, they'd probably catch it if I rewrote the Founder's axioms." – Veronica Santangelo
- "Shield yourself from those not bound to you by steel, for they are the blind. Aid them when you can, but lose not sight of yourself, it says."Arthur Maxson in Fallout 3.
- "Fear those who do not pledge to the Brotherhood for though their eyes may be opened through service, they are now blind."
- "Give way your suspicions to the wisdom of thine Elder. Where he shows trust, so shall you."
- "Through discourse, we gain the strength of our Brothers' minds."Cross in Fallout 3.
- "We do not help them, or let them in. We keep knowledge they must never have." – Recited by Nolan McNamara in Fallout: New Vegas.