Vault 39 is one of the Vault-Tec vaults, located in what was known as Abilene before the Great War and is now called Lone Star.
The Vault's original purpose in the Vault experiment is unknown. Due to Reese's experiments with the G.E.C.K., it now basically houses a jungle, with huge mutated plants and plant walls, hostile to all other life forms.
This vault is very similar to Vault 22 in the Mojave Wasteland, except Vault 22 had no G.E.C.K.
