Excerpts from Sky Dancer
Female Buddha Tsogyel explains that women must contain their rising sexual energy, that is, their "red bodhicitta," just like men, if they would cultivate spiritual enlightenment. (Men have "white bodhicitta.")
[ If there is leakage of bodhicitta, the Buddha Unchanging Light is slain...Therefore, with the power of retraction, drawing up 'love' with the base energy of life-force, I held it in the pot of my belly, and maintaining the recollection of pleasure uncontaminated by lust, divesting myself of mind-created samadhi yet not slipping into an instant of torpor, I experienced the ascent of Awareness.
Commentary by Tibetan Buddhist scholar Keith Dowman:
Joy is created by the ascent of the blended red and white bodhicittas up the medial nerve from the sexual centre through the gut, heart, throat and head centres in turn (although the most intense feeling of joy is in the gut and the least intense in the head). The rising bodhicitta is kundalini....
Refined semen is stored in the heart centre as "radiance," which produces long-life and gives a shine to the complexion. Unrefined semen is excreted during sexual intercourse and is, of course, procreative seed. The refined semen in the heart centre permeates the body as Awareness; "heart centre" is here a metaphor for the all-pervasive sphere of essential being (dharmakaya). Loss of semen, by any means, causes the life-span to be shortened and causes a pallid complexion....Loss of semen is equated with killing a Buddha. Semen, seed-essence and bodhicitta are synonymous. After initiation, intensity of desire is essential to force the bodhicitta up the medial nerve; not only is desire vitiated by orgasm, but the will to enlightenment itself is temporarily lost....
Strip the yoga of its arcane terminology and there is a simple meditation technique: stimulate desire and then use it as the object of meditation and it becomes Awareness - a fuel of Emptiness and pure pleasure....
Whether or not an embodied 'mystic partner' is present to intensify desire and stimulate the bodhicitta [sexual essence], there is no trace of the hedonistic indulgence. Sexual pleasure as erotic play, intimate dalliance, orgasm or even coitus interruptus has no place in this yoga. The equation of sexual indulgence and the Buddhist Tantra has been formed by misguided, commercially motivated individuals pandering to the prurient neuroses of the sexually jaded seeking titillation in the arcane sex of obscure religious cults. "Do not be loose with your sexual organs," advises [female Buddha] Tsogyel. "Bind them fast." And "Preserve the seed of kindness for the sake of other beings." No zap-lam sexual yoga can be accomplished without attaining control of energy on every level - a traditional metaphor compares the muscular control of a yogin or yogini sucking up the blended bodhicittas, and retracting the elixir from the sexual centre, to a duck drinking water...
Selfless sexuality and heightened sensory awareness are the keys to sexual satisfaction....
The woman, or rather, the Dakini, transforms the man who lusts after her into her Guru, the man of her dreams....It is the Dakini's nature of complete receptivity, empty space, that assuages male aggression....
Even the uninitiated can gain intimation of pure gnostic awareness in the post-coitus hiatus, when our 'mystic partner' and all external phenomena seem to float in space, and sound has a clarity and timbre unrecognised in ordinary perception. The samaya of the Fourth Initiation is to sustain this experience of the 'natural purity in the world of appearances'.
It is the essential genius of Tantra that the most basic and most powerful of human instincts is used as a skillful means to stimulate, or expand, awareness and create insight into the nature of reality, and to generate the will to selfless service.... 
NAMO GURU PADMA SIDDHI HRI!
My sons you have met a sublime consort, the Great Mother,
And by virtue of your resources of accumulated merit,
Fortuitously, you have received the four empowerments.
Concentrate upon the evolution of the four levels of joy.
Immediately you set eyes upon my body-mandala,
Your mind was possessed by a lustful disposition,
And your confidence won you the Vase Initiation.
Apprehend the very essence of lust,
Identify it as your creative vision of the deity,
And that is nothing but the Yidam deity himself.
Meditate upon lustful mind as Divine Being.
Uniting with space, your consort's secret mandala,
Pure pleasure exciting your nerve centres,
Your aggression was assuaged and loving kindness was born,
And its power won you the Mystic Initiation.
Apprehend the very essence of joy,
Mix it with your vital energy and maintain it awhile,
And if that is not mahamudra, nothing is.
Experience pleasure as mahamudra.
Joined to your consort's sphere of pure pleasure,
Inspired to involuntary exertion,
Your mind merged with my mind,
And that blessing won you the Wisdom Initiation.
Undistracted, guard the very essence of pleasure,
Identify pure pleasure with Emptiness,
And that is what is known as immaculate empty pleasure.
Experience pure pleasure as supreme joy.
United at your consort's blissful nerve,
Our two nectars fused into one elixir.
The phenomena of self and others extinguished,
Awareness won you the Initiation of Creative Expression.
Guard the natural purity in the world of appearances,
Identify your love and attachment with Emptiness,
And that is nothing other than Dzogchen itself.
Experience innate joy as no-joy.
This is extraordinary, exalted secret instruction;
To consciously practise this method brings a fall,
But discovered by chance it gives miraculous release.
You attained the four empowerments at once,
And your success was matured by the four stages of joy.1
Excerpt from "What Is Tantra, Anyway? (Ask the Lama Surya Das)"
Lama Surya Das
Of course, sexuality is a healthy part of life, and the sexual drive is one of the most powerful energies in us. Although Western religions seem to have lost touch with the wisdom of the body and the sacred dimension of sexual energy, Tantric adepts through millennia have worked to find ways in which to integrate that energy into spiritual practice, and turn this powerful force into rocket-fuel-like propellant on the path of spiritual ecstasy and transcendence. In ancient India, this became the practice known as sacred sex, practiced with a certain amount of ritual and using specific ritual sexual practices, including maithuna - coupling with minimal movement, and holding of or even abstaining from orgasm in order to increase self-control and to purify desire.
This practice - given the right intention, training, guidance, concentration, and conditions - can sublimate and tansmute sexual drive into higher, more spiritual aspirations. Through practices known as seminal retention, "melting and blazing," the "all-consuming fire of total embrace," "mystic heat," and so forth, advanced practitioners have been able to redirect the release of energy upward through the body, opening all the chakras in continuous waves of full-body, orgasm-like bliss and consciousness. Quite a contrast - in purpose and experience - to the more typical, brief, downward-releasing sexual climax, usually followed by dullness and sleep. 
Excerpt from Being Peace
Thich Nhat Hanh, Buddhist monk (not Tantric)
[By bringing a child into the world] you continue the cycle of suffering. Aware that having more children in his society would be to make them suffer, the Buddha urged the monks not to have children. 
14th Mindfulness Training
(and commentary by Thich Nhat Hanh, Buddhist monk)
[quote=14 Mindfulness Trainings] The Fourteenth Mindfulness Training: Right Conduct
(For lay members): Aware that sexual relations motivated by craving cannot dissipate the feeling of loneliness but will create more suffering, frustration, and isolation, we are determined not to engage in sexual relations without mutual understanding, love, and a long-term commitment. In sexual relations, we must be aware of future suffering that may be caused. We know that to preserve the happiness of ourselves and others, we must respect the rights and commitments of ourselves and others. We will do everything in our power to protect children from sexual abuse and to protect couples and families from being broken by sexual misconduct. We will treat our bodies with respect and preserve our vital energies (sexual, breath, spirit) for the realization of our bodhisattva ideal. We will be fully aware of the responsibility of bringing new lives into the world, and will meditate on the world into which we are bringing new beings.
(For monastic members): Aware that the aspiration of a monk or a nun can only be realized when he or she wholly leaves behind the bonds of worldly love, we are committed to practicing chastity and to helping others protect themselves. We are aware that loneliness and suffering cannot be alleviated by the coming together of two bodies in a sexual relationship, but by the practice of true understanding and compassion. We know that a sexual relationship will destroy our life as a monk or a nun, will prevent us from realizing our ideal of serving living beings, and will harm others. We are determined not to suppress or mistreat our body or to look upon our body as only an instrument, but to learn to handle our body with respect. We are determined to preserve vital energies (sexual, breath, spirit) for the realization of our bodhisattva ideal.
[quote=Thich Nhat Hanh]So many individuals, children, couples and families have been wounded by sexual misconduct. Practicing this training is to prevent ourselves and others form being wounded. Our stability and the stability of our families and society depend on it. To practice the Fourteenth Mindfulness Training is to heal ourselves and our society. When we are determined in this effort, the energy that is formed helps us transform into a bodhisattva. This is mindful living. In Buddhism, we speak of the oneness of body and spirit. What happens to the body also happens to the spirit. The sanity of the body is the sanity of the spirit; the violation of the body is the violation of the spirit. The union of two bodies can only be positive when there is also understanding and communion on the level of the spirit.
Sexual communion should be a ritual performed in mindfulness with great respect, care, and love. True love contains care and respect. It is deep, beautiful, and whole. In my tradition, husband and wife are expected to respect each other as guests, and when they practice this kind of respect, their love and happiness will continue for a long time. In sexual relationships, respect is one of the most important elements.
True love also includes a sense of responsibility, accepting the other person as they are, with all their strengths and weaknesses. The expression “long-term commitment” helps us understand the word “love.” A long-term commitment between two people is only the beginning. For a tree to be strong, it needs to send many roots deep into the soil. If a tree has only one root, it will be blown over by the wind. The life of a couple also needs to be supported by many elements – families, friends, ideals, practice, and Sangha. Understanding this training in the context of community is very important.
“Responsibility” is the key word. We need mindfulness in order to have that sense of responsibility. In a community of practice, if there is no sexual misconduct...there will be stability and peace. We refrain from sexual misconduct because we are responsible for the well-being of so many people...
We need to discuss problems relating to the practice of this training, like loneliness, advertising, and even the sex industry. The feeling of loneliness is universal in our society. When there is no communication between ourselves and other people, even in the family, the feeling of loneliness may push us into having sexual relationships. The belief that having a sexual relationship will help us feel less lonely is a kind of superstition. In fact, we will be more lonely afterwards. When there is not enough communication on the level of heart and spirit, a sexual relationship will only widen the gap and destroy us both. Our relationships will be stormy, and we will make each other suffer.
In practicing the 14th Mindfulness Training, we should always look into the nature of our love to see and not be fooled by our feelings. Sometimes we feel that we have love for the other person, but maybe that love is only an attempt to satisfy our egoistic needs. Maybe we have not looked deeply enough to see the needs of the other person. He or she should not be looked on as an object of our desire or some kind of commercial item. Sex is used in our society pervasively as a means of selling products. There is also the sex industry. These things are obstacles to our practice. We must remember to look at one another as human beings with the capacity of becoming a Buddha.
After several years of ascetic practice, Shakyamuni Buddha realized that mistreating the body was a mistake, and he abandoned that practice. He saw that both indulging in sensual pleasure and mistreating the body were extremes to be avoided, that both led to degeneration of mind and body. As a result, he adopted the Middle Way between the two extremes.
In Asia, we say that there are three sources of energy—sexual, breath, and spirit. Sexual energy is the type of energy that we expend during sexual intercourse. Vital breath energy is the energy we expend when we speak too much a breathe too little. Spirit energy is the energy we expend when we worry too much.
We need to know how to maintain the balance, or we may act irresponsibly. According to Oriental medicine, if these three sources of energy are depleted, the body will weaken and disease will appear. The it will be more difficult to practice. In Taoism and also in the martial arts, there are practices for preserving and nourishing these three sources of energy.
When practicing conscious breathing—counting the breath or following the breath—we do not waste the vital breath energy, instead we strengthen it. Concentration and the enjoyment of meditation do not expend spirit, but strengthen it. You can learn ways to channel your sexual energy into deep realizations in the domains of art and meditation.
In the Buddha's time, a typical monk was a quiet person who practiced walking and sitting meditation both day and night...This way of life enabled him to preserve both vital breath and spirit. In the time of the Buddha, the main reason for monks abstaining from sexual activity was to preserve energy. This is a point of commonality between Buddhism and most other Eastern spiritual traditions. During the most difficult periods of nonviolent struggles, Mahatma Gandhi also practiced abstinence, and he advised his colleagues to do the same in coping with tense, difficult situations. Strength of spirit depends on these three sources of energy. In Vietnam, the word “spiritual” is formed by combining the words for sexual energy and spirit. The material and the spiritual are no longer distinct, and the name of each is used for the other. Those who have fasted know that if the three sources of energy are not preserved, you cannot fast for long. IN 1966, the monk Thich Tri Quang fasted in Vietnam for one hundred days, because he knew how to preserve his three sources of energy.
A second reason that monks in the Buddha's time refrained from sexuality was to cut off the “chain of rebirth.” (samsara) The first meaning or rebirth means to be reborn in our offspring... During the time of the Buddha, much moreso than in our own time, poverty and disease were the common lot for most people. This situation is reflected in the First Noble Truth. Imagine a family with too many children, all of them frail and ill. There is a permanent shortage of food, no medicine, and no means of contraception. Each year a new child is born. This is still common in many parts of the our world, and both parents and children suffer. Rebirth must be understood in this context and with this background. For these people, a new birth is often not a joy, but a catastrophe. To give birth to a child is to perpetuate the cycle of hunger and disease. This is the continuation of samsara. The mindfulness training for celibacy during the time of the Buddha also aimed at preventing childbirth; it had a birth-control function.
Therefore, this mindfulness training is directly related to issues of population, hunger, and economic development. The presence of Buddhist monks in countries like Sri Lanka, Burma, Thailand, Laos, Cambodia, China...and Japan for more than 20 centuries has contributed significantly to reducing the world's population by billions. The population explosion is one of the most serious problems of our day. Hunger leads to war and, in our times, wars are incredibly destructive. Countries that cannot control their populations cannot overcome poverty. And there is the threat of nuclear holocaust. Parents must be aware of the actual situation in the world. We should know the future into which we are sending our children, to motivate us to act and live in a way that can create a better future for ourselves and our children.
We must be clearly aware of the responsibility we bear in bringing new life into the world. The answer is not to stop having children, but to make the world a better place. The future of the Earth and our children depends on the way we live today. If we continue to exploit and destroy our ecosystems, if we allow the arms race to continue, if we do not curb the growth of the world's population, the Earth and humankind will not have a future. Each of our ways of life can be a brick for building a future of peace. The Fourteenth Mindfulness Training is vast... To understand and practice this training deeply, we have to the relationship between it and and our daily meditation practice, the Four Noble Truths, and the Buddhist teaching on rebirth.
Finally, Buddha himself said
Enlightenment resides in the sexual parts of women. ("Buddhatvam Yosityonisamasritam.")
Taken together with Thich Nhat Hanh's remark above, it may be that Buddha was hinting at the power of controlled intercourse.
The Metta Sutta by Buddha
This is what should be done
By one who is skilled in goodness,
And who knows the path of peace:
Let them be able and upright,
Straightforward and gentle in speech.
Humble and not conceited,
Contented and easily satisfied.
Unburdened with duties and frugal in their ways.
Peaceful and calm, and wise and skillful,
Not proud and demanding in nature.
Let them not do the slightest thing
That the wise would later reprove.
Wishing: In gladness and in safety,
May all beings be at ease.
Whatever living beings there may be;
Whether they are weak or strong, omitting none,
The great or the mighty, medium, short or small,
The seen and the unseen,
Those living near and far away,
Those born and to-be-born,
May all beings be at ease!
Let none deceive another,
Or despise any being in any state.
Let none through anger or ill-will
Wish harm upon another.
Even as a mother protects with her life
Her child, her only child,
So with a boundless heart
Should one cherish all living beings:
Radiating kindness over the entire world
Spreading upwards to the skies,
And downwards to the depths;
Outwards and unbounded,
Freed from hatred and ill-will.
Whether standing or walking, seated or lying down
Free from drowsiness,
One should sustain this recollection.
This is said to be the sublime abiding.
By not holding to fixed views,
The pure-hearted one, having clarity of vision,
Being freed from all sense desires,
Is not born again into this world.
- Sky Dancer: The Secret Life and Songs of the Lady Yeshe Tsogyel, Keith Dowman, Snow Lion Publications (1996), pp. 42, 234, 248-51.
- What Is Tantra, Anyway? (Ask the Lama Surya Das) Lama Surya Das recommends the following writing on Tantra:
Tantra: The Path of Ecstasy by Georg Feurstein, World of Tantra by B. Bhattachary. Also, the many writings of Chogyam Trungpa Rinpoche, including The Lion's Roar: An Introduction to Tantra
- Being Peace, Thich Nhat Hanh, Parallax Press (1987).
- 1. From Sky Dancer pp. 118-19, Chapter. Seven:
Establishing, Spreading and Perpetuating the Teaching.