are a series of massive underground fallout shelters developed by Vault-Tec Industries
in the mid-21st century. Construction of the vaults averaged at billions of dollars (an extraordinary amount even when considering the hyperinflation present during the mid-2000's), so occupants were forced to pay exorbitant prices if they sought entrance. Those that secured their place in a vault were saved from the horrors of the Great War
but led to often worse fates within the vaults. Rather than intending to save citizens of the United States
, the true, sinister reason is that these 'shelters' were in fact a series of sociological experiments conducted by the Enclave
. Each vault was set up with different conditions, and then observed to see how the dwellers within coped with the controlled conditions in isolation. Only seventeen of the vaults had no ulterior motive and were designed to preserve humanity, while Vault 0
monitored all of the vaults and their occupants.