Invitation is a weakness of vampires and hybrids, including Original Vampires. In order for a vampiric being to enter any house owned by humans, witches, werewolves, or (human) doppelgängers, they must be invited by the owners of the home.
Once invited, the vampire cannot be uninvited unless the ownership of the house changes.
Television Series vs. Book Series
Television SeriesThis protection appears to manifest itself as an invisible barrier that automatically erects itself on the door lintels and any available entrance in a human home if a vampire tries to enter that dwelling without an invitation from the owner. It is essentially as though a witch has placed a magical boundary spell on the threshold that no vampire can pass through.
An invitation into a home may also come from someone who is either currently residing in the house or who has in the past, as they are, by extension, also receiving ownership from the actual owner(s). This extended ownership even continues long after a person who has lived in the house for a significant amount leaves, and an invitation into a home can be extended even over the phone from thousands of miles away. This was demonstrated by Jo Laughlin, who invited Stefan Salvatore into the Parker House despite the fact that she hadn't been there in almost twenty years, and that she was in Mystic Falls, Virginia while he was 3,000 miles away in Portland, Oregon.
These invitation barriers are extremely strong, as they are among the few known ways to keep vampires at bay, if killing the owner is not an option. The barrier only holds for as long as the vampire remains uninvited, the owner(s) remain alive, and the dwelling remains standing. If the vampire is invited in, the barrier magically disappears, and if the owner dies or is killed, the house will no longer have an invitation barrier so long as the house's ownership doesn't revert to another person, such as if it's left to a family member in a will. If a homeowner dies and is then resurrected, the magical invitation barrier is "deactivated" despite the owner returning to life, and it is unknown if the ownership can be refreshed in the case that this should happen.
Vampires who are unable to convince a human to invite them into their home have often been known to resort to other methods to enter the house, such as setting the house on fire to either destroy the home or to drive the humans inside out of the house and the protection it provides. Other methods of destruction will often yield the same effect, such as when Klaus Mikaelson started throwing fence pikes through the Gilbert House when he wasn't immediately extended an invitation.
Vampires have been known to use this weakness to their advantage by establishing a home with a human owner so as to keep other unfriendly vampires from gaining access to their homes without invitation. Some vampires even go so far as to compel their human title-holders not to give a specific vampire entry, such as when Frederick compelled Miss Gibbons not to allow Damon Salvatore to enter her home, where Stefan was being held captive and tortured.
Ownership can apparently be tampered with, as the magical protection is based on signed legal documents. This was seen when the Salvatores opted to bestow ownership the Salvatore Boarding House to Elena Gilbert so she could use it as a safe house after Klaus came to Mystic Falls. Elijah Mikaelson was able to bypass the protection of the Guerrera Mansion in a similar manner by (presumably) compelling a city official to invoke imminent domain upon the home, giving it heritage status and therefore making the home open to the public without invitation.
If the ownership of a home changes while a vampire is still inside, there can be very violent side effects. For example, in The Dinner Party, Elijah was daggered and brought into the Salvatore Boarding House while the house was still in the name of the deceased Zach Salvatore and could be entered by any vampire without invitation. However, while Elijah was kept daggered and unconscious in the basement cellar of the house, the Salvatore brothers had a lawyer transfer ownership to Elena in order to use it as a "safe house" from any vampires who try to hurt or abduct her for Klaus. When Elena undaggered Elijah some days later, Elijah immediately became disoriented upon reawakening and was unable to breathe, which made it difficult to properly control his body during his desperate attempts to get out of the house, causing him to accidentally into several walls in his frantic attempt to leave the house. It seems unlikely that a fully conscious vampire could be forced into a house where they had not been invited.
A vampire who is conscious and in the home of a human when the ownership changes, the vampire will be violently ejected from the house by a magical force. This was demonstrated in Never Let Me Go, when Lily Salvatore transferred the deed to the Salvatore Boarding House to her housekeeper Lucy to prevent the Mystic Falls Gang from rescuing Caroline. Stefan and Caroline were both still inside the boarding house at the time, and the former was forcibly yanked backward out the doors to the balcony and into the backyard below, while Caroline was pulled out into the hall and down the stairs by an invisible force until the housekeeper finally invited Caroline in, stopping the ejection process.
However, there do seem to be loopholes to this weakness for very rare vampiric beings. For example, the true immortal Silas was able to enter homes of non-vampires without invitation, but this is most likely due to the fact that while immortals do survive on the blood of the living, Silas was still alive and therefore was undead like vampires and hybrids. It has also been hinted that Klaus's daughter could possibly be immune to this particular vulnerability of vampires as well, since she was born a hybrid and is fully alive rather than undead, and as such, she is capable of owning land/property.
Unlike its TV counterpart, vampires can enter homes into which they are invited in by anyone in the house at the time, whether they're the owner, a resident, or a guest. However, if a house contains old structures of the original house along with renovated portions of the house that were added much later, the vampire must be invited into those parts of the house by only the original owners; for example, Elena Gilbert said that her bedroom and the living room are part of the original house, so Katherine von Swartzschild, Damon Francesco Salvatore and Stefan Antonio Salvatore cannot enter these rooms, as the original owners are no longer living and are unable to invite them in.
In Klaus, it is shown that while a vampire who has been invited into a house cannot technically have their invitation revoked, there is a loophole to this rule-- if the ownership of a house changes, then the vampire will have to be re-invited by the new owner. If a vampire is desiccated or unconscious when the ownership changes, such as in the case of the daggered Elijah, the vampire will become disoriented and will begin to feel as though they are suffocating until they are able to flee from the house.
In Never Let Me Go, it is shown that vampires in a house that changes ownership will be pulled by an invisible force until they are out of the house, and they will need to be re-invited to gain entry. This was demonstrated when the ownership of the boarding house changed while Stefan and Caroline were still inside, causing Stefan to be pulled backward and out the glass doors into the yard while Caroline was pulled downstairs toward the front door.
In The Devil Comes Here and Sighs, it is shown what happens to a vampire who is forced to enter a home uninvited when Aurora held Cami into Lucien's Penthouse. Immediately, she experienced extreme pain and bled from her eyes and nose. It was presumed that this would have eventually killed Cami. However it should be noted that this was a barrier spell placed on his penthouse, where only members of Klaus's sireline could enter without an invitation and not a true invitation barrier. Therefore, it is possible the effects was due to the fact that it was a spell and is still currently unknown what happens to a vampire who passes through a home uninvited.
- The idea that vampires need to be invited to enter homes or residences has different meanings, but the principle is mostly the same "Protection against undead".
- In some stories, vampires can not enter homes because it is inhabited by living things, and it's like being underwater, murky and full of life.
- In The Vampire Diaries, vampires were not created by Nature compared to the other species. As a defense, Nature weakens the vampires with sunlight, wood, vervain, and other elements (for example, running water weakens vampires in the books). With the purpose to defend against the undead, the living kept the vampires away by banning them entry into their homes. Literally, it's like saying: "I invite my own death to my home".
- The origin of inviting a vampire into a home is in the novel Dracula by Bram Stoker. It is mentioned that Dracula was always invited to the homes, causing suspicion about this feature because in those days, people of a high social class invited other people of the same class as a form of education and respect. Because Dracula looked, talked and moved like a person of high social statue, it was easy for him to gain an invitation into others' homes.
- In A View to a Kill, when Bonnie trapped Niklaus in the Gilbert House, it was a reference to the books.
- In the books, Elena's bedroom and living room are part of the original construction of the house, and because of this, and vampires cannot enter these places, as they cannot obtain permission from the original owners.
- Hope Mikaelson is the first living hybrid. Therefore, she is able to own property and likely has immunity from invitation.
- In Where Nothing Stays Buried, Van Nguyen mentions to Lucien Castle how invitation is different from magic. Therefore cannot be used to grant access, only invitation of the owner can.