[[Image:SMOrg9th.jpg|thumb|right|Organization Organisation of a Codex-Compliant Space Marine [[Chapter]] since the introduction of [[Primaris Space Marines]]{{Fn|20a}}]]

The Codex Astartes was a code developed by Guilliman. This tome would contain everything a member of the Astartes would need to know to function. From recruitment to organization organisation to tactics and beyond the Codex Astartes became a sacred text to the majority of the Chapters.{{Fn|10}} One of the most significant changes under the new Codex was the newly founded Chapters. Where the Legions could number more than 10,000 strong the Chapters would be limited to about a thousand. Each original Legion would be divided as many times as needed into successor Chapters. This division would come to be called the [[Second Founding]] seven years after the Horus Heresy{{Fn|11b}}, in 021.[[M31]]. The remaining thousand bodies in the original Legion would also survive as a new Chapter of the same name. While these newly created Chapters claimed their founders origins, such as their Primarch, they would also come to develop their own culture and customs.{{Fn|25a}}

Vehicles attached to While a company will generally bear the company's colour and number in a small roundel somewhere on the hullwould normally consist of ten squads, as well as attached squads can form an identifier number to distinguish between different attached vehicles of the same type.{{Fn|26c}} Transport vehicles attached to a specific squad also bear that squad's heraldryadditional ten, including squad number and battlefield role insigniataking up designations as squads 11-20.{{Fn|26c35a}}

While [[Apothecaries]] and [[Chaplains]] are usually permanently part of a company would normally consist of ten squadsCompany, while [[Librarians]] and [[Techmarines]] are considered attached squads can form an additional tento the Company but ultimately belong to the [[Librarius]] and [[Armoury]], taking up designations as squads 11-20respectively.{{Fn|35a37}}

Members The left shoulder plate of a Space Marine's Power Armour usually shows the Marine's Chapter Badge, while the right displays squad typically bear that markings. Squad markings in a Codex-compliant Chapter consist of a squad's number laid over a battlefield role icon and squad number on their right pauldrons. [[Close Support Squad]]s utilise display a 4-way arrowto designate their battlefield role, while [[Fire Support Squad]]s display an inverted V known as a chevron, and [[Battleline Squad]]s use a simple upwards-facing arrow. [[Space Marine Command Squad|Command Squads]] bear a skull, and [[Veteran Squad (Space Marines)|Veteran Squads]] use a stylised version of the [[Crux Terminatus]] similar to a Cross Pattée. [[Space Marine Veteran|Veterans]] in [[Terminator Armour]] wear a real [[Crux Terminatus]], albeit on their left shoulder pads, displacing their Chapter Badges to their right pauldron.{{Fn|20a}}{{Fn|27a}} Some Chapters choose to display squad information on other parts of the armour, e.g. on kneepads.{{Fn|18b}}{{Fn|18c}}

Squads in Battle Companies are numbered so that squads 1-6 are Battleline, squads 7-8 are Close Support, and squads 9-10 are Fire Support. However, squads 11-20 from Reserve Companies attached to a Battle Company don't appear to follow any required format, meaning they could all be Close Support squads, for example.{{Fn|20a}} The Vanguard squads in the 10th Company also don't follow the same strict numbering scheme that the battle companies do, so it's possible to have a Battleline 10th squad in a Codex-compliant 10th Company.{{Fn|41}} ====Squad Markings=Vehicles and Dreadnoughts===The left shoulder plate of a Each Codex-compliant Space Marine'Company maintains a permanent number of [[Dreadnought]]s Power Armour almost always shows and transport tanks, and can requisition more from the MarineChapter [[Armoury]].{{Fn|20a}} Vehicles attached to a company will generally bear the company's Chapter Badge. The right pad shows colour and number in a small roundel somewhere on the squad badgehull, as well as an identifier number to distinguish between different attached vehicles, this indicates although the type exact meaning of identifier numbers vary.{{Fn|Note 2}}{{Fn|26c}} Transport vehicles attached to a specific squad also bear that squad's heraldry, including squad the marine belongs to number and the number of his squad within the companybattlefield role insignia. {{Fn|26c}} Aircraft are usually organised into squadrons, which are structured similarly to Space Marine squads, except with [[Veteran SquadTechmarine]]s use piloting (usually 3) aircraft instead of infantry. Squadrons are led by a stylised version wing leader, who combines the function of the a [[Crux TerminatusSpace Marine Sergeant|Sergeant]] similar and a Techmarine. Squadrons are also often attached to a Cross PattéeCompanies, Tactical Squads use an arrowand bear that company's insignia. While there is no official marking scheme for squadrons, Assault Squads use four perpendicular arrows pointing outwards aircraft are usually marked with large blocks of colour on the wings and Devastator Squads use an inverted V known as a chevrontail for easy identification from long distances, with the wing leader's aircraft featuring the most ornate design. Space Marines Numbers applied to aircraft's hulls can also be used to differentiate between aircraft in Terminator Armour wear the [[Crux Terminatus]] on their left padsame squadron, and their Chapter Badge on their right padwith the wing leader usually being numbered 1.{{Fn|27a40}} Squad numbers are typically superimposed on the squad type insignia Battlefield roles can be given to aircraft, but many chapters choose to display them on other parts of with some having the armour, e.g. on kneepadsclose support role.{{Fn|18b40}} Aircraft can form mixed-type units, such as a Storm Wing, which contains a [[Stormraven Gunship]] escorted by two [[Stormtalon Gunship]]s.{{Fn|18c40}}

[[Techmarine]]s are Space Marine engineers and mechanics,{{Fn|27h}} and can also function as pilots for some of a Chapter's larger vehicles, such as aircraft. {{Fn|40}} They wear red armour, irrespective of what chapter they belong to, and wear their Chapter Badge as normal.{{Fn|27h}}