Charisma

 is one of the seven Primary Statistics in the SPECIAL character system.

Fallout, Fallout 2 and Fallout Tactics
In Fallout 2, Charisma also determines the number of base companion slots your character is given. This number is equal to your charisma score divided by two, rounded down. For example, if you have 5 Charisma, you can recruit 2 followers. You can still recruit 1 follower at 1 charisma, however.

Predesigned Primary Charisma-based Characters (PPCC) of Fallout are Albert, and in Fallout 2's case, Chitsa.

In Fallout Tactics, Charisma, at best, is a secondary trait. Due to the nature of the game (i.e. almost exclusively combat-based) it is feasible to complete the game easily with 1 or 2 Charisma with no penalty. It is involved with the Barter skill and is required for the Leader perk. A low Charisma, on the other hand, gives access to the Loner perk.

Ways to increase Charisma in Fallout

 * Find the Singer random encounter. Speaking with Patrick the Celt and having a high enough Speech will increase Charisma by one.
 * Pop some Mentats for a temporary +1 Charisma.

Ways to increase Charisma in Fallout 2

 * Install the blue memory module into ACE, then request the following surgery. Your Charisma will be increased by one.
 * Take the Gain Charisma perk for another one point.
 * Having the mirrored shades, obtained from Mason (Salvatore's Bar, you have to kill him) or one of the graves in Golgotha, active in one of your item slots increases Charisma by one.
 * Pop some Mentats for a temporary +1 Charisma.

Fallout 3
Modifies: Speech and Barter Skills, NPC Disposition

Charisma increases the disposition of all NPCs, which makes speech checks easier. Disposition is also affected somewhat by karma (most NPCs like good characters more), quests (doing a quest in a way an NPC likes can dramatically boost disposition), and dialog options (being a jerk in conversations can lower disposition a little). Charisma also affects the Barter and Speech skills. Characters who use speech will want at least a decent charisma, but adding points to the skill is almost always better than adding points to the score. Characters who do not use the speech skill have little use for this SPECIAL score.

There are also general Charisma checks in dialogue with some characters, in addition to Speech checks. Avoid wearing things like Enclave Power Helmets, as they deduct 1 point of charisma whilst equipped.

Ways to increase Charisma

 * The Charisma Bobblehead can be found on a table in Vault 108's cloning lab in a room with beds.
 * The Intense Training perk will allow you to increase your Charisma (or any other S.P.E.C.I.A.L. stat) once for each time that you take it.
 * The following clothing will increase Charisma by 1 for each piece worn.
 * Eulogy Jones' suit and hat (+2 Charisma, +2 Small Guns)
 * Regulator duster (+1 Charisma, +5 Small Guns)
 * Sexy sleepwear (+1 Charisma)
 * Sheriff's duster (+1 Charisma, +5 Small Guns)
 * Tenpenny's suit (+1 Charisma, +2 Small Guns)
 * Vance's longcoat outfit (+1 Charisma, +1 Perception, +10 Small Guns)
 * Three Dog's headwear (+1 Luck, +1 Charisma)
 * All alcoholic beverages give a temporary +1 CH (-1 IN, +1 ST, +2 CH in the case of moonshine) bonus, albeit harbouring the danger of addiction.
 * Ant queen pheromones (+3 Charisma)
 * Grape Mentats give a temporary +5 Charisma

Fallout: New Vegas
Charisma in New Vegas modifies Barter, Speech and Companion Nerve. Companion Nerve gives each companion in the party +5% to their damage and armor, up to a maximum of +50% at 10 Charisma.

Regardless of Barter or Speech level, some interactions will not be available if your Charisma is too low (Ex. Corporal Betsy). These ultimately do not have any significant effect on game play, nor do they provide any special bonuses.

Ways to increase Charisma
Food, Drink, and Drugs:
 * Alcohol, +2
 * Whiskey, +1
 * Mentats, +1
 * Party Time Mentats, +5 (and can stack with normal Mentats)
 * Ant queen pheromones, +3

Clothing: Perk:
 * Sexy sleepwear, +1
 * T-51b Power Armor helmet, +1
 * Sheriff's Duster, +1
 * Vera's Outfit +1
 * Bounty Hunter Duster +1
 * Charisma Implant +1
 * Intense Training