The fundamental thing to know about tantric sex is that it's based on a loose collection of religious texts in Sanskrit known as tantra that come from the non-mainstream of Hindu, Buddhist, and Jain tradition. The tantra were very much, in other words, challenging normal religious practice, and haven't necessarily had the best reputation throughout their existence.

They're also heavily focused on a lot of different things, from magic rituals to spells and mantras. Their overall perspective is complicated, but is often based on the idea that concentration can evoke relevant deities inside people and unleash their spiritual energy. They also emphasize that the body needs to be used to reach higher states of consciousness, maybe through yoga, or through gratification. Sex, as Loriliai Biernacki notes in "The Yogini and the Tantric Sex Rite," is sometimes not a high priority in the tantra; ones focused on yoga don't mention it at all, and it's not nearly as "ubiquitous" among tantra texts as you might imagine.

What's sex got to do with it? Well, there are a few answers for this. One is that the interaction of male and female bodies is meant to represent and embody male and female gods, Siva and his Goddess, and through the process of sexy sex-times, people could concentrate on "being" these holy figures, channel their energy, and get closer to enlightenment and salvation. In some early tantra traditions, it gets pretty specific: it's about sexual fluid.

Historian David Gordon White, in "Transformations in the Art of Love," says that it was all about both semen and lady-moisture:

"In these earlier or peripheral traditions, it was via a sexually transmitted stream or flow of sexual fluids that the practitioner tapped into the source of that stream, the male Siva... Siva does not, however, stand alone in this flow of sexual fluids. Here, his self-manifestation is effected through his female hypostasis, the Goddess, whose own sexual fluid carries his divine germ plasm."

These days, most tantric sex emphasizes "semen retention," or the practice of not coming for ages and ages to build up spiritual energy. It's a radical departure.

The fact that we conceive of tantric sex as a sex thing and not a religion thing comes from a few things. One of them is undoubtedly the fact that we first learned about it in the West from the writings of horrified Christian missionaries who witnessed practitioners doing rituals involving eating meat and other "forbidden" practices. The French missionary Abbe Dubois, who published a book on his travels through India and elsewhere in 1807, noted in disgust:

"Among the abominable rites practiced in India is one which is only too well known; it is called sakti-puja; sakti meaning strength or power. Sometimes it is the wife of Siva to whom this sacrifice is offered; sometimes they pretend that it is in honor of some invisible power. The ceremony takes place at night with more or less secrecy. The least disgusting of these orgies are those where they confine themselves to eating and drinking everything that the custom of the country forbids, and where men and women, huddled together in indiscriminate confusion, openly and shamelessly violate the commonest laws of decency and modesty."

Other missionaries would write with horror of other bits of ritual Tantric practice, all, of course, in contrast to the expected chastity and purity of Christianity. Our picture of tantric sex as delightful and decadent probably dates from the horrified Abbe.

You've got to remember that the tantras weren't mainstream practice, and were often highly disapproved of or seen as sacrilegious. One theory about how they may have emerged came out of the works of Sanskrit scholars like Benoytosh Bhattacharyya in the early 20th century, who thought that tantra practices turned up because monks in early Buddhist monasteries were degenerates. It was a popular view for a long time: scholars of Buddhism thought that this intensely distasteful and subversive bunch of practices may have turned up because "official" Buddhism may not have been sufficient for quelling the urges of monks when it came to sex and indulgence, so they made up their own "rites" to compensate. We're now not entirely sure that's the case, but it's a hilarious theory.

Want to know how tantra landed in our consciousness? The answer is, well, a bit odd: a Victorian-era occultist once called "the wickedest man in the world." Aleister Crowley was the most notorious figure of Victorian Europe and dabbled in any mystic tradition he could get his hands on, including, it seems, tantra and tantric sex. Crowley, it seems, saw sex as a supreme source of magical power, though he may or may not have known a lot about tantra as a whole. It's likely through him (he wrote about it a lot) that the association between sex and tantra became so firm in the Western imagination. (The Sanskrit texts had earlier been translated by Sir John Woodroffe, an Orientalist, who for some reason decided he could only write them under the name Arthur Avalon.) Since then, even though figures like Alexandra David-Neel, a formidable French traveller who became an expert in tantra in the late 19th century and lived an eccentric life in a Tibetan monastery, have come and gone in tantra's history, the legacy of its presence in the Western imagination is a Sting quote and a host of sexual pleasure articles.

As you may have picked up, what we now view as "tantric sex," and Tantra in general, is pretty different from what's actually in the texts and how it was practiced.

"As early as the romantic era, the "mystic Orient" has been imagined as the exotic world of forbidden sexuality and dark sensuality," Hugh Urban notes in Tantra: Sex, Secrecy, Politics, and Power In The Study Of Religion, adding that a lot of our interpretation of the tantras comes from our own weird stuff about sex in the Western world, particularly in the Victorian era, when they first appeared via colonial translations.

David Gordon White goes further. He notes in Kiss Of The Yogini that today's tantric sex industry is basically a "funhouse mirror-world," in which "Indian practitioners and gurus take their ideas from Western scholars and sell them to Western disciples thirsting for initiation into the mysteries of the East." The fundamental difference, he points out, is that tantra, when it applies to sex at all, is about the sexualization of ritual, not the ritualization of sex. It was often meant to make certain rituals sexy for specific reasons in context, not to make the act of sex itself somehow spiritual and awesome.