In the fictional world of the television series Buffy the Vampire Slayer and its spin-off series Angel, a vampire is a unique variety of demon that can exist on the earthly plane only by inhabiting and animating a human corpse. They are also called Lonely Ones, Van-Tal, and Lurks.

Vampires in the canonical Buffyverse differ significantly from their counterparts in the 1992 Buffy the Vampire Slayer movie. While the movie's vampires possess the ability to fly, maintain a relatively human appearance, and do not disintegrate into dust upon death, the vampires introduced in the first episode of the television series are portrayed as demonic spirits that inhabit human corpses.

According to Rupert Giles, an occult expert in the series, when an ancient race of demons called the Old Ones were banished from Earth, the last one fed on a human and mixed their blood, creating the first vampire. This vampire then fed on other humans and made more of its kind, essentially becoming a biological weapon for the Old Ones against the human race. According to Illyria, a character in Angel, vampires existed during her time as an Old One—long before the rest were banished from the realm. Because of their partly human nature, vampires are considered impure by other demons.

The series vampires exhibit superhuman abilities, including increased strength, heightened senses, and accelerated healing. These powers intensify as they age or when they consume the blood of powerful supernatural beings. Vampires live indefinitely without aging, with the oldest losing the ability to appear human. Vampires can change at will between human appearance and a monstrous form with a pronounced brow ridge, yellow eyes, and sharp teeth. This transformation can happen in seconds. In human form, they can be detected by their lack of heartbeat and lower body temperature. They do not cast reflections, although they can be photographed and filmed.

Vampires in the series possess all the memories and skills of their human predecessors. They also retain much of their host's personality, including any mental illnesses or emotional instabilities. For example, Spike (unlike most vampires) retained his love for his dying mother. Harmony kept her valley girl personality and her love of unicorns. Darla tells the newly turned Liam/Angelus that "what we were, informs what we become"; after her resurrection as a human, she says that the darkness he unleashed as Angelus was always in him as a human, long before they met, resulting from memories of abuses by his father. Most vampires in the Buffyverse do not have human souls, but they are capable of feeling human emotions, such as love—though these tend to be expressed as twisted and obsessive behavior—and without souls, they typically can only experience the negative affectivity associated with evil. In the episode "The Harvest", Giles says the human corpse a vampire is born into is infected with a demon soul via vampiric blood, and therefore lacks a conscience. Some vampires, such as Angel and Spike, have their human souls restored to them, bringing remorse for their previous actions.

Vampires in the Buffy universe live on a diet of blood, preferring fresh human blood; they can distinguish the blood of different animals by flavor, and those who do not drink human blood enjoy that of otters. They require no other food or drink; although they can ingest it, they generally find it bland. Prolonged deprivation of blood can impair a vampire's higher brain functions and they become "living skeletons", but do not die. They do not need to breathe air—although they can breathe to speak or smoke—and they cannot pass breath on to others via CPR. They are affected by drugs, poisons, and electricity, and they can be sedated and tasered. Some vampires in the series enjoy recreational drug use like alcoholic and caffeinated beverages, and tobacco—Spike, the witty "bad boy" vampire, frequently enjoys smoking cigarettes, and Angel frequently drinks coffee and tea to cope his restless lifestyle.

To reproduce, vampires must drain a human being of most of their blood, then force the victim to drink some of the vampire's blood. This process is known as "siring", and the vampire who does so is called a "sire". Sires often act as mentors to their 'children', and form small covens of related vampires for various purposes. Some vampires can be telepathically linked to those that they have sired. The amount of time it takes for a new vampire to rise seems to vary; Buffy often kills vampires as they rise from their graves, but other vampires rise after only a few hours.

The vampires in Buffy heal quickly from most injuries, but do not regrow lost limbs, and can acquire scars. They can be killed if beheaded, exploded, staked through the heart with a wooden object, or exposed to sunlight, fire, or excessive amounts of holy water. When killed, vampires rapidly turn to dust. Their vulnerability to sunlight limits vampires' movements, and makes most nocturnal. Spike, however, is shown on several occasions driving during the day by blocking the sunlight coming through his car windows with foil, and leaving a small strip clear to see the road. Vampires sometimes enlist humans such as criminals or occult organizations like Wolfram & Hart for tasks during the day.