The Patimokkha describes the basic set of rules followed by ordained members of Buddhist communities. These rules apply to all monks and nuns enrolled in schools of Buddhism, although the forms and scriptures differ somewhat. The following is excerpted from the Pail version which is upheld by the Shravakayana or Theravada traditions.
It is important to note that such rules applies only to monks and nuns - in other words, those who have entered into that stage of training. Ordained monks and nuns adopt these rules in order to provide them with the opportunity to prepare themselves for the higher levels of the path, within which the sexual function must be dealt with in order to reach complete enlightenment. For such a demanding and difficult work, the person must be very well prepared. Thus, the rules as follows were developed. Unfortunately, most of the contemporary schools have forgotten that this was the original purpose of having monks and nuns: to prepare them for the sacred ritual of sexual union.
While there are eight levels of rules, from the most serious down to minor ones, we quote here from the two most serious rules: (1) parajika (which means "defeat"); and (2) sanghadisesa (which means and requires a "formal meeting" of the community or sangha). What is most striking here is that of all the rules outlined in this lengthy treatise, the very first - and thus most important ones - concern sex. This is evidence of the central importance of sex in spiritual life.
Buddhist Monastic Code I: Parajika
Rule 1. Should any bhikkhu [ordained person] — participating in the training and livelihood of the bhikkhus, without having renounced the training, without having declared his weakness — engage in the sexual act, even with a female animal, he is defeated and no longer in communion.
Buddhist Monastic Code I: Sanghadisesa
Here, venerable Sirs, the thirteen matters, which, as well in their earlier as in their later stages, require formal meetings of the Order, come into recitation.
2. Should any bhikkhu, overcome by lust, with altered mind, engage in bodily contact with a woman, or in holding her hand, holding a lock of her hair, or caressing any of her limbs, it entails initial and subsequent meetings of the Community.
3. Should any bhikkhu, overcome by lust, with altered mind, address lewd words to a woman in the manner of young men to a young woman alluding to sexual intercourse, it entails initial and subsequent meetings of the Community.
4. Should any bhikkhu, overcome by lust, with altered mind, speak in the presence of a woman in praise of ministering to his own sensuality thus: "This, sister, is the highest ministration, that of ministering to a virtuous, fine-natured follower of the celibate life such as myself with this act" — alluding to sexual intercourse — it entails initial and subsequent meetings of the Community.