"Zen asserts, as do other schools in Mahayana Buddhism, that all
sentient beings have Buddha-nature, the universal nature of inherent
wisdom (Sanskrit prajna) and virtue, and emphasizes that Buddha-nature
is nothing other than the nature of the mind itself. The aim of Zen
practice is to discover this Buddha-nature within each person, through
meditation and mindfulness of daily experiences. Zen practitioners
believe that this provides new perspectives and insights on existence,
which ultimately lead to enlightenment.

In distinction to many other Buddhist sects, Zen de-emphasizes
reliance on religious texts and verbal discourse on metaphysical
questions. Zen holds that these things lead the practitioner to seek
external answers, rather than searching within themselves for the
direct intuitive apperception of Buddha-nature. This search within
goes under various terms such as “introspection,” “a backward step,”
“turning-about,” or “turning the eye inward.”

In this sense, Zen, as a means to deepen the practice and in contrast
to many other religions, could be seen as fiercely anti-philosophical,
iconoclastic, anti-prescriptive and anti-theoretical. The importance
of Zen's non-reliance on written words is often misunderstood as being
against the use of words. However, Zen is deeply rooted in both the
scriptural teachings of the Buddha Siddhārtha Gautama and in Mahāyāna
Buddhist thought and philosophy. What Zen emphasizes is that the
awakening taught by the Buddha came through his meditation practice,
not from any words that he read or discovered, and so it is primarily
through meditation that others too may awaken to the same insights as
the Buddha.

The teachings on the technique and practice of turning the eye inward
are found in many suttas and sutras of Buddhist canons, but in its
beginnings in China, Zen primarily referred to the Mahayana Sutras and
especially to the Lankavatara Sutra. Ironically, since Bodhidharma
taught the turning-about techniques of dhyana with reference to the
Lankavatara Sutra, the Zen school was initially identified with that
sutra. It was in part through reaction to such limiting identification
with one text that Chinese Zen cultivated its famous non-reliance on
written words and independence of any one scripture. However, a review
of the teachings of the early Zen masters clearly reveals that they
were all well versed in various scriptures. For example, in The
Platform Sutra of the Sixth ancestor and founder Huineng, this
famously "illiterate" Zen master cites and explains the Diamond Sutra,
the Lotus Sutra, the Vimalakirti Sutra, the Shurangama Sutra, and the
Lankavatara Sutra.

When Buddhism came to China the doctrine of the three core practices
or trainings, the training in virtue and discipline in the precepts
(Sanskrit Śīla), the training in mind through meditation (dhyana or
jhana) sometimes called concentration (samadhi), and the training in
discernment and wisdom (prajna), was already established in the Pali
canon.[14] In this context, as Buddhism became adapted to Chinese
culture, three types of teachers with expertise in each training
practice developed. Vinaya masters were versed in all the rules of
discipline for monks and nuns. Dhyana masters were versed in the
practice of meditation. And Dharma, the teaching or sutra, masters
were versed in the Buddhist texts. Monasteries and practice centers
were created that tended to focus on either the vinaya and training of
monks or the teachings focused on one scripture or a small group of
texts. Dhyana or Chan masters tended to practice in solitary
hermitages or to be associated with the Vinaya training monasteries or
sutra teaching centers.

After Bodhidharma's arrival in the late fifth century, the subsequent
dhyana-chan masters who were associated with his teaching line
consolidated around the practice of meditation and the feeling that
mere observance of the rules of discipline or the intellectual
teachings of the scriptures did not emphasize enough the actual
practice and personal experience of the Buddha's meditation that led
to the Buddha's awakening. Awakening like the Buddha, and not merely
following rules or memorizing texts became the watchword of the dhyana-
chan practitioners. Within 200 years after Bodhidharma at the
beginning of the Tang Dynasty, by the time of the fifth generation
Chan ancestor and founder Daman Hongren (601-674), the Zen of
Bodhidharma's successors had become well established as a separate
school of Buddhism and the true Zen school.[15]

The core of Zen practice is seated meditation, widely known by its
Japanese name zazen, and recalls both the posture in which the Buddha
is said to have achieved enlightenment under the Bodhi tree at Bodh
Gaya, and the elements of mindfulness and concentration which are part
of the Eightfold Path as taught by the Buddha. All of the Buddha's
fundamental teachings—among them the Eightfold Path, the Four Noble
Truths, the idea of dependent origination, the five precepts, the five
aggregates, and the three marks of existence—also make up important
elements of the perspective that Zen takes for its practice. While
Buddhists generally revere certain places as a Bodhimandala (circle or
place of enlightenment) in Zen wherever one sits in true meditation is
said to be a Bodhimandala.

Additionally, as a development of Mahāyāna Buddhism, Zen draws many of
its basic driving concepts, particularly the bodhisattva ideal, from
that school. Uniquely Mahāyāna figures such as Guānyīn, Mañjuśrī,
Samantabhadra, and Amitābha are venerated alongside the historical
Buddha. Despite Zen's emphasis on transmission independent of
scriptures, it has drawn heavily on the Mahāyāna sūtras, particularly
the Heart of Perfect Wisdom Sūtra, Hredaya Pranyaparamita the Sūtra of
the Perfection of Wisdom of the Diamond that Cuts through Illusion,
The Vajrachedika Pranyaparamita the Lankavatara Sūtra, and the
"Samantamukha Parivarta" section of the Lotus Sūtra.

Zen has also itself paradoxically produced a rich corpus of written
literature which has become a part of its practice and teaching. Among
the earliest and most widely studied of the specifically Zen texts,
dating back to at least the 9th century CE, is the Platform Sutra of
the Sixth Patriarch, sometimes attributed to Huìnéng. Others include
the various collections of kōans and the Shōbōgenzō of Dōgen Zenji.

Zen training emphasizes daily practice, along with intensive periods
of meditation. Practicing with others is considered an important part
of Zen practice. D.T. Suzuki wrote that aspects of this life are: a
life of humility; a life of labor; a life of service; a life of prayer
and gratitude; and a life of meditation.[16] The Chinese Chan master
Baizhang (720–814 CE) left behind a famous saying which had been the
guiding principle of his life, "A day without work is a day without
food.""

http://en.wikipedia.org/wiki/Zen