The Sangha of monks and the Sangha of nuns were originally established by Gautama Buddha in the 5th century BC in order to provide a means for those who wish to practice the Dhamma full time, in a direct and highly disciplined way, free from the restrictions and responsibilities of the household life.
The Sangha also fulfils the function of preserving the Buddha’s original teachings and of providing spiritual support for the Buddhist lay-community.
The monastic sangha has historically assumed responsibility for maintaining the integrity of the doctrine as well as the translation and propagation of the teachings of the Buddha.
The key feature of Buddhist monasticism is the adherence to the vinaya which contains an elaborate set of rules of conduct including complete chastity and eating only before noon.
Between midday and the next day, a strict life of scripture study, chanting, meditation, and occasional cleaning forms most of the Sangha's duties . Transgression of rules carries penalties ranging from confession to permanent expulsion from the Sangha.
The founder of Japanese Tendai decided to reduce the number of rules down to about 60 (Enkai).
In Kamakura Era, many sects (Zen, Pureland and Nichiren) that originated from Tendai sect abolished vinaya entirely. Therefore Japanese Zen, Pureland and Nichiren, are led by priests (or minister) rather than by monks.
Monks and nuns may own only the barest minimum of possessions due to their samaya as renunciates (ideally, three robes, an alms bowl, a cloth belt, a needle and thread, a razor for shaving the head, and a water filter).
In practice, they often have a few additional personal possessions.
Traditionally, Buddhist monastics eschew ordinary clothes and wear robes. Originally the robes were sewn together from rags and stained with earth. The idea that robes were dyed with saffron seems unlikely to be true since it was and still is a very expensive commodity, and monks were poor.
The color of modern robes varies from community to community (saffron is characteristic for southeast Asian Theravada and Mahayana groups, maroon in Tibet, gray in Korea, black in Japan etc.)
The word which is usually translated as monk is bhikkhu in Pali or bhikshu in Sanskrit. The feminine form is bhikkhuni or bhikshuni.
These words literally mean "beggar", learner, auspicious, adept, endowed with harmony and order; and it is traditional for bhikkhus to beg their food.
In most places this has become an elaborate ritual, where lay people feed monastics in order to obtain merit which will ensure them a fortunate rebirth.
Although monastics in India traditionally did not work for income, this changed when Buddhism moved to east Asia, so that in China and the surrounding countries monks often engage in agriculture.
The idea that all Buddhists, especially monks and nuns practice vegetarianism is a Western misperception.
In some Sanskrit Mahayana Sutras meat eating is strongly discouraged.
In Pali Canon the Buddha rejected a suggestion by Devadatta to impose vegetarianism on the Sangha. According to the Pali Texts, the Buddha ate meat .
According to the Mahayana Sutras, the Buddha does not eat meat. The Buddha allowed Sangha members to eat whatever food is donated to them by laypeople, except that they may not eat meat if they know or suspect the animal was killed specifically for them.
Consequently, the Theravadan tradition (Sri Lanka, Thailand, Laos, Cambodia and Burma) which follows the Pali scriptures does not practice vegetarianism though an individual may do so at his or her personal choice .
On the other hand, the Mahayana and Vajrayana traditions accept both Theravada and Mahayana scriptures, and consequently the practice will vary depending on their interpretation of the sutras.
In particular, East Asian monastics take on the bodhisattva vows from the Brahma Net Sutra which has a vow of vegetarianism as part of the Triple Platform Ordination where they receive the sramanera/sramanerika, bhikshu/bhikshuni and bodhisattva vows, whereas the Tibetan lineages transmit the bodhisattva vows from Asanga's Yogacarabhumi, which does not include a vow of vegetarianism.
In some areas such as China, Korea and Vietnam one expects the Sangha to practice strict vegetarianism while in other areas such as Japan or Tibet one does not.
The lay community is responsible for the production of goods and services in society, and for the production and raising of children.
According to Mahayana sutras, the Buddha always maintained that lay persons were capable of great wisdom in the Buddhadharma and of reaching enlightenment.
In the west, there is a misconception that Theravada regards enlightenment to be an impossible goal outside the Sangha.
This is incorrect. In Theravada suttas, it is clearly recorded that the Buddha's uncle—who was a lay follower—reached enlightenment by hearing the Buddha's discourse.
The distinction between Sangha and lay persons has always been important and forms the Parisa, Buddhist community.
Here, monastics teach and counsel the laity at request while laymen and laywomen offer donations for their future support. This inter-connectedness serves as a marriage and has sustained Buddhism to this day.