Citadels are a type of player-built structure, and were introduced during the Citadel expansion (April 2016). They are intended to replace the functionality of starbases and Outposts, allowing players the same functionality of a station such as docking, storing of items, refitting and corporation offices while also being expanded with the use of service modules to allow Clone Bay, Market and Reprocessing functionality.
There are currently three different sizes of citadels; the medium Astrahus, the large Fortizar and the extra-large Keepstar.
There's also the very rare (only one can ever exist at a time) Upwell Palantine Keepstar.
Anchoring a citadel
- Main article: Anchoring structures
In order to anchor a citadel you'll need a ship with an appropriately sized cargo hold or fleet hangar, the right roles and a suitable spot to anchor your citadel. After that the whole building process, while automatic, takes 24 hours.
With the Citadel anchored you will now see it listed in the overview and be able to warp to it if you are not already on grid it will also be displayed on the directional scanner. A number of lights will now have appeared around it. Most are for show with the exception of a ring of lights around the edge indicating the docking ring.
Upon docking you will be able to switch between an exterior view of the citadel or the ship hanger. In addition if permitted you will be able to take control of it loading the overview and allowing you to manage the citadels fittings.
As with a normal station you have a personal item and ship hanger along with corporation hangers if they have rented an office in the citadel. While in control of a citadel you will be able to access the Ammo Bay, Fuel Bay and Fighter Bay
Station Services such as Cloning can be accessed in the same method but will be locked and un-selectable if the appropriate service module is not fitted and online. These service modules consume fuel to maintain and when first onlined will immediately use 72 hours worth of fuel.
While in control of a citadel you are able to target objects that are not invulnerable, deploy fighters and activate offensive modules as you would if you were in control of a ship using the same safety settings.
- Fighter hangar is 100.000m³. It's possible to overload the fighter hangar i.e. you can switch between squadrons although the hangar and launch tubes are completely full.
- Jump Clones can be left in citadels located in wormhole space with the appropriate service module but you cannot jump to them while outside of that system
- Disabling a Cloning Centre does not destroy installed jump clones but prevents the activation of them.
- In addition attempting to clone to a Medical Clone at a Citadel with a disabled Cloning Centre you will be rerouted to your corporation HQ.
- Main article: Tethering
Tethering allows players with permission to dock in the citadel to remain in space without being targetable, essentially making them invulnerable. While tethered the structure will also repair any damage modules fitted to your ship and drones currently in your drone bay. While you can move around as long as you stay close to the structure, several actions break the tether as well as stops you from tethering to begin with.
- Main article: Vulnerability States
You cannot attack a citadel unless it's in its vulnerability state. Citadels go in and out of vulnerability states depending on how the owners have set up its vulnerability hours, with the Astrahus being vulnerable for 3 hours, the Fortizar for 6 hours and the Keepstar for 21 hours.
- See also: Asset Safety
Upon destruction of a Citadel it offlines, becoming a wreck and ejects all online players with their active ship. The wreck remains behind ejecting a Hanger Container that holds dropped loot from the Citadel.
Player and Corporation assets (items, ships, etc) that were stored in the Citadel can be recovered at a different station through the Asset Safety system.
- Additional test needed for players that are offline when destroyed.
Difference in Citadels
Astrahus: Medium citadel, only allows subcapital ships to dock, Unable to fit Market Service Module, 20,000m3 Ammo Bay, Unable to use Guided Bomb Launcher, Point Defence, Doomsday, 3 vulnerable hours per week.
Fortizar: Large citadel, allows subcapital and capital ships to dock, unable to use Doomsday, 6 vulnerable hours per week.
Keepstar: Extra-Large citadel, allows all ships to dock, able to fit all citadel modules, 21 vulnerable hours per week.
Groups and the Structure Browser: both are found in the Business menu of the neocom 
The group will start with you in the admin role, and you can add more Character/corp/alliances by dragging them from people and places menu or any other place like chat or a linked name
The roles in the group are in order Admin > Manager > Member > Blocked.
A character can be given any of the roles, while Corporation and Alliances can only be given the member and blocked roles.
You can add the "public"(the globe icon) to a group but it can only be given the member role. Admins can add remove any of the rolls including other admins, while managers can only add/remove people from the member and blocked roles
Blocked are on the black list even if they are a member of one of the corp with access
Groups can be shared in chat by dragging them. These group are then Use by structure profiles in the Structure Browser 
To start creating and editing profiles go to the 'My Structures' tab 
Click on the New profile Button 
Before assigning any structures to this new profile I will add group to each roll on the profile setting tab
the different groups are in order Docking, Defense, Clone Bay, Corporation Office, Market and Reprocessing.
Defense is taking control of a citadel and is the only way to get it to shoot.
You can add a group to a role by Clicking on the + sign.
Click save after adding the groups
It’s as easy as changing this value in the profile settings (isk for Clone bay and Corporation offices)(% for market tax and Refining tax) other galactic taxes may apply 
Fitting a Citadel
Fitting a citadel is much like fitting a ship: if you have the roles required to take control of a citadel, you can just open up the fitting window and drop module in just like a ship. 
To 'online' the service you must have fuel in the fuel bay which only seems accessible while controlling the citadel.  This is the same with the fighter bay (which works like the carrier version, if not more buggy) and the ammo hold (if you want the Missile/bomb launcher to reload automatically the ammo must be place in there  
- Warping to a citadel at 0 while it is anchoring can cause ships to become stuck. This has a higher likelihood of happening with larger ships.
- It is not possible to jump from a clone in known space to a clone in wormhole space or vice versa. Medical Clones cannot be set inside wormhole space.
- It is however possible to swap clones in any type space; including wormhole space. I.e. dock at a citadel in a wormhole where you have a jump clone installed then jump into that clone and leave your current clone installed at that citadel instead. Doing this does not incur the normal 24 hour cooldown on using a jump clone.
- Micro Jump Field Generators will not move any ship that is tethered including the ship that activated the module.