Fallout 4 Companions

Overview
The base game offers 13 unique permanent companions, each with their own quirks and storyline. Automatron adds two new, fully-customizable robot companions. Both Far Harbor and Nuka-World introduce a single, narrative-focused companion. The total number of companions is 17.

List of temporary companions
The game has a number of temporary companions that will only be available during certain quests.

Affinity
Affinity only applies to permanent companions. General behavior

Miscellaneous actions

Faction activities

Bugs

 * A companion may become stuck in a reference pose position, flying around unanimated about 1–2 feet off the ground following the player character. The companion can be spoken with and interacted with in a normal manner, however, the companion will not fight. Even loading a new area by going through a door will not fix this behavior.
 * One potential fix is to fast travel to another location.
 * Another fix is to dismiss the companion. The companion can be re-recruited back.
 * Certain sound effects can get "stuck" to companions and continue to play after said companion quit performing the respective action. Known examples include the sound of wielding a Ripper, firing a Gauss rifle, Dogmeat's bark and using the weapon bench's drill. When the bug occurs it follows the companion around, waxing and waning depending on their distance, and can neither be stopped by fast-traveling, reloading, or taking the weapon away from them. It can, however, be fixed by closing and restarting the game. It is currently unknown what exactly causes the bug.
 * Should the Ripper sound be playing over and over, having the companion use the weapon again may fix the bug.
 * If a companion has the drilling-sound glitch from an armor workbench or weapon workbenches, allowing them to re-use the corresponding workbench from where the glitched sound is and let them end its use by themselves without interruptions, the sound glitch should stop and be fixed.
 * Even after dismissing Dogmeat, he may continue barking. A possible fix for this is to turn on Classical Radio and then turn it off.
 * Ada may remain with you even though you have just selected dismiss in dialogue, as well as the option of the settlement won't pop up.
 * One solution is to restart the game.
 * Another solution is to acquire a different companion.
 * When sending a companion to another settlement using the workshop he/ she will not go there straight away, and bringing the settlement choices back up will show the place still has an option to where they can be sent.
 * A fix for this is to turn the game off, then reloading the save.
 * Another fix is to fast travel to a different place and sleep in a bed and return.
 * If a companion is down while changing zones, they may remain "downed" permanently, only changing areas along with the Sole Survivor. This can be fixed by damaging their HP until they go "down" and regenerate again while out of combat.
 * Having a romanced companion giving the Lover's Embrace perk, while they are wearing power armor, can result in a bug, where fusion cores are being completely drained upon exiting any power armor.

Behind the scenes
Another companion was planned for the Nuka-World add-on, voiced by Orion Acaba, though he was cut from the final release.