A Werewolf is a human who transforms into a wolf-like figure on nights of the full moon in the fictional Buffyverse established by Buffy the Vampire Slayer and Angel.

ORIGINS
A person becomes a werewolf when they are bitten by another werewolf and survive. It doesn't matter whether the werewolf is in human or in wolf form. From this point on, the victim transforms into a lupine creature and remains so from sunset to sunrise during the three nights of the full moon, or alternatively from moonrise to moonset, depending on species. When transmuted, the human side of the psyche is completely dormant, taken over by a feral predatory mentality that knows only the hunt.

BIOLOGY
Werewolves are capable of "sensing strong emotions", sometimes from miles away, by perceiving the release of hormones and pheromones - which is why they are attracted by "sexual heat". They can track more successfully than bloodhounds by sheer scent. They can also perceive the presence of other werewolves even if they're in human form.

The psyche of a young werewolf remains separate between the human self and the feral side. The traumatic and painful experience of the transformation causes the werewolf to lose memory of it, until some sort of evidence provides conscious knowledge of the person's condition, such as waking up naked in a different place from the one in which the transformation took place.

Even after the werewolf acknowledges its condition, he or she retains no memories of whatever action they might take during the transformation. The lupine beast, completely dominated by instinct, is incapable of recognizing loved ones or friends. The wolf side does, however, exert influence on the basic instincts and impulses of the werewolf while in human form.

Older werewolves, unlike younger ones, are capable of retaining memories following the transformation into human form. Prior to this phase of the werewolf's life, it is also possible for the werewolf to exert certain influence on its actions during the feral phase.

The werewolf curse, so far, remains impossible to cure. However it is possible to control the transformation. Monks in Tibet taught Oz meditation techniques that they combined with herbs in his diet, along with chanting and charms. He's now able to roam about under a full moon in apparent ease and comfort. However, intense negative stimulation such as great physical pain or overly stressful social situations can trigger the transformation, even during the day, as seen later with Oz.

Silver is the most effective way to kill a werewolf, but other severe injuries might be enough to do the job. Oz was able to kill Veruca by tearing into her throat with his fangs. However, it is common in Werewolf fiction that the fangs and claws of other Werewolves(And sometimes other supernatural beings in general) are almost as effective as Silver. There is presently no way to know for sure if this was the case when Oz killed Veruca. Like vampires, werewolves can be affected by drugs and tranquilizers, although the exact dosage required for both cases is never specified. Tranquilizers are sometimes employed to restrain free-roaming werewolves without injuring them.

PSYCHOLOGICAL AND SOCIAL ISSUES
While some werewolves try to hold their animalistic impulses in check, other werewolves believe that their human side is merely a disguise, a cage for their true selves, and do not restrain in any way. Whether a werewolf chooses to embrace its condition or not, it depends on a number of social and psychological factors, it can't be sorely blamed on the influence from the bestial side of the werewolf psyche.

Both Oz and Nina, after learning of their condition, seek out ways of restraining themselves during their transformations in order to protect people, especially their loved ones.

Veruca, unlike Oz, relishes in her werewolf condition, believing it to be her true self. She refuses to be locked during her transformation and lets her instincts and impulses dominate every one of her actions, whether in human or in lupine form. She believes that doing what comes naturally is good and desirable, even it these impulses include killing.

McManus originally tried to protect people from himself. He abandoned his family and tried to remain away from people. Eventually he gave up and returned to populated areas. Unlike Oz or Nina, he lacked the support necessary to cling on to his humanity.

The existence of werewolf packs is mentioned. These groups seemingly hold similar beliefs to those of Veruca and sometimes kidnap young werewolves to increase their ranks.

On the side of humans, reaction to the existence of werewolves is extremely varied:

Gib Cain hunts down werewolves in lupine form to skin them and sell their fur. He doesn't care that his victims are humans for the rest of the month.

Scoobies and Angel's crew argue that werewolves can't be held accountable for their actions in lupine form. They do make an exception to this belief when it comes to werewolves that, knowing of their condition, do not seek any method of restraint, regarding these individuals as they would regard common vampires and demons, or at least a dangerous human.

Certain parties and individuals hold werewolves as abominations and seek to eliminate them.

Paranormal sporting groups capture werewolves to hunt them down in events, similar to foxhunting in England.

Werewolf flesh is also considered a delicacy in certain circles. Werewolves are captured, cleaned, restrained and served alive, as the particular sub-species of werewolf coveted for its meat, Lycanthropus Exterus, will revert back to human form after dying.

SPECIES
There are more than one species of Werewolf. In "Unleashed", Nina Ash contracts lycanthropy from a breed of Werewolf never seen before in North America called Lycanthropus Exterus. Thus Nina is a different species of werewolf to that of Oz and Veruca. As far as we can tell from what is seen on both BtVS and AtS, the more common Werewolf is smaller, with a heavy coat of fur, and while still being very dangerous, doesn't have a large mouth or canine set of teeth. The Lycanthropus Exterus on the other hand walks on two legs, has longer, more powerful arms, is larger and sports a snout and canine fangs. It is unknown if the varying breeds have different strengths and weaknesses, or if their differences are mostly cosmetic. The non-canon Buffy RPG assumes the former.

KNOWN WEREWOLVES

Jordy

Daniel "Oz" Osbourne

Veruca (deceased)

McManus (deceased)

Nina Ash

WEREWOLF-RELATED BUFFYVERSE EPISODES

"Phases"

"Beauty and the Beasts"

"Wild at Heart"

"New Moon Rising"

"Unleashed"

CONTINUITY ERRORS/RETCONS
In "Phases", the physical characteristics of the werewolf are completely different from those in "Beauty and the Beasts" and afterwards, where the werewolf looks more human-like. This is merely a change in continuity that ignores the "Phases" look. A similar change took place in the Star Trek universe, where the Trill race never again appeared as they did in their first appearance.

Another continuity error/change involves the status of werewolves after death. "Unleashed" establishes that werewolves revert back to human form upon death, whereas in the episode "Phases" we see Cain carrying teeth and pelts from the werewolves that he has killed. A retcon in the later episode seems to establish that different species of werewolf react differently.