Talk to the guard to be able to join Vault City

Go to Vault City and talk to the guard at the gate to the inner city. Depending on your stats and skills he will require different things of you in order to join Vault City as a citizen. This guard is the one person who can grant you Vault City Citizenship.

NOTE: If you become a Vault City "citizen", thus by joining the Vault City NPC faction, you will be automatically removed from whatever faction in which you were already a member, and this will happen with no prompts. Switching factions has caused some people confusion in the past, so if you're already in a faction, understand this before engaging this dialogue option.

Talking with the Guard

• If your Intelligence is 4 or less, he will treat you as if you're a total idiot.
• If your IN is 5 or more, you are treated better but IN alone is not enough to gain citizenship.

Requirements to Join the Vault City Faction

• If your Charisma is higher than 8, you can beg the guard to be let in successfully.
• Otherwise he may give you a quest to retrieve the Hydroelectric Magnetosphere Regulator from the reactor in Gecko to gain citizenship.
• If those options are not available, you can gain access if you have any of these:
  • Repair 125 is not good enough on its own to become a citizen
  • First Aid 200 is not good enough on its own to become a citizen
  • Doctor 200 is not good enough on its own to become a citizen
  • Science 125 is not good enough on its own to become a citizen
• If your character doesn't see any of the above dialog options to join Vault City faction, Kama Sutra Master support perk gives special dialog option with guard, to let you join.

NOTE: If you want to do the quest, "collect rent for the guard" (requires Speech 100?), then do it before joining the Vault City faction, because it is not available to Vault City citizens.

Limited Visitation

There is another way to be allowed inside the city area at Vault City, and that is to get a Day Pass. A Day Pass means you're just a visitor, and not a citizen member of the Vault City faction, but you're allowed to go in past the gate and do commerce with merchants inside the city. Just remember, with a Day Pass, you're an authorized visitor during daytime hours only and you must be out on time or you'll be shot. With a Day Pass, you're not allowed to be inside the city after hours, nor are you allowed inside the vault at all, as vault access is only for actual "citizens".

Rewards

• Joining the Vault City faction (Access to the inner city and Vault 8). You are now a Vault City citizen !