Perhaps the single most notorious characteristic of the vampire is his penchant for drinking blood. Most dead creatures (ghosts, demons …) in the Indo-European and Semitic world are considered thirsty, not just vampires. While some dead were content with any liquid offered, vampires almost always choose blood.

Alan Dundes suggests that aging and dying are correlated to dehydrating; the same way a ripe plum shrivels into a prune. He further hypothesizes that people, therefore, assumed that the dead would be thirsty since they are dried out. This belief led to the practice of pouring libations on graves to appease the dead. This belief was later applied to vampires who went looking for their offerings.

Another answer is that the dead's craving for liquids is not merely to regain the appearance of youth, but to give them life again, blood being the supreme elixir of life.

Blood both fascinates us and repulses us; it simultaneously represents purity and impurity, the sacred and the profane, life and death. Little wonder then that it is heavily used in religious, magic rituals as well as art creation.

When shamanism is associated with women, blood letting during menstruation is an important part of 'walking with the spirits'.  Followers of the cult of Kali in India often drink blood. Sisir Das, a practitioner of Hindu occult rituals, drank the goats' blood of 207 sacrificed goats at the Kali temple in Bengal's Midnapore district over the course of four days.

Throughout history the many liquid substances (milk, honey and wine) offered in sacrifice to the dead, to spirits and to gods, were symbols of blood. Sacrificial blood was itself obtained from animals in classical times, and from human sacrifice among Asians, Africans, aboriginal Americans, and from prehistoric Europeans.

In a similar fashion, the history of art is full of images of blood, from the representations of wounded animals in the cave paintings of Lascaux to the most recent representations of extreme Body Art.

In his book 'Violence and the Sacred', Rene Girards' theory of sacrifice states,

"The physical metamorphoses of spilt blood can stand for the double nature of violence...Blood serves to illustrate that the same substance can stain or cleanse, contaminate or purify, drive men to fury and murder or appease their anger and restore them to life"
(Girard, 1972)

Blood plays an important role in the modern vampyre subculture. Some clans partake of blood drinking and bloodletting. A group of members who imbibe blood are referred to as a "feeding circle" and as opposed to media articles they do not bite each other on the neck but usually use razor blades to make cuts into each other’s bodies and suck the blood from those cuts.

Some other popular customs of vampire clans include fetishism, sadomasochism and bondage. This is inspired by the myth of the Vampyre as hunter. Participants are referred to as Regnant (master) and Thrall (slave). The "safe word" that interrupts every S/M play is substituted by a "True Name" for vampyres. That means that if someone knows the (chosen) True Name of a vampyre, he or she has power over their action (and therefore can stop it).

Blood is the vital element of the vampire; he cannot survive without feeding with fresh blood. As every myth, the vampire is related to the eternal struggle between Life and Death, Good and Evil and it is no wonder if we find a lot of parallel between the Myth of the Vampire and Christian symbols.

It is the reason why the vampire's blood-drinking habits are not only considered a perversity of human morality, but also of Christianity.

At Communion, the priest recites the following before giving wine– symbolic of blood– to the congregation:

“The Blood of our Lord Jesus Christ, which was shed for thee, preserve thy body and soul unto everlasting life. Drink this in remembrance that Christ's Blood was shed for thee and be thankful.”

The vampire’s communion is an inversion of the Christian’s one. Rather than drinking Christ's immortal blood, the vampire drinks the blood of the mortal. Rather enjoying his eternal life in the hereafter, he spends it on earth.