According to discourses found in both the Theravada school's Pali canon and the Agamas (a class of early Buddhist school sutras that were preserved in the Chinese Mahāyāna tradition), the Noble Eightfold Path was rediscovered by Gautama Buddha during his quest for enlightenment. The scriptures describe an ancient path which has been followed and practised by all the previous Buddhas. The Noble Eightfold Path is a practice said to lead its practitioner toward self-awakening and liberation. The path was taught by the Buddha to his disciples so that they, too, could follow it.
In the same way I saw an ancient path, an ancient road, traveled by the Rightly Self-awakened Ones of former times. And what is that ancient path, that ancient road, traveled by the Rightly Self-awakened Ones of former times? Just this noble eightfold path: right view, right aspiration, right speech, right action, right livelihood, right effort, right mindfulness, right concentration...I followed that path. Following it, I came to direct knowledge of aging & death, direct knowledge of the origination of aging & death, direct knowledge of the cessation of aging & death, direct knowledge of the path leading to the cessation of aging & death...Knowing that directly, I have revealed it to monks, nuns, male lay followers & female lay followers...
The practice of the Noble Eightfold Path varies from one Buddhist school to another. Depending on the school, it may be practiced as a whole, only in part, or it may have been modified. Each Buddhist lineage claims the ability to implement the path in the manner most conducive to the development of its students.
 The threefold division of the path
The Noble Eightfold Path is sometimes divided into three basic divisions, as follows:
Division Eightfold Path factors Acquired factors
Wisdom (Sanskrit: prajñā, Pāli: paññā) 1. Right view 9. Superior right knowledge
2. Right intention 10. Superior right liberation
Ethical conduct (Sanskrit: śīla, Pāli: sīla) 3. Right speech
4. Right action
5. Right livelihood
Concentration (Sanskrit and Pāli: samādhi) 6. Right effort
7. Right mindfulness
8. Right concentration
This presentation is called the "Three Higher Trainings" in Mahāyāna Buddhism: higher moral discipline, higher concentration and higher wisdom. "Higher" here refers to the fact that these trainings that lead to liberation and enlightenment are engaged in with the motivation of renunciation or bodhicitta.
 The practice
According to the bhikkhu (monk) and scholar Walpola Rahula, the divisions of the noble eightfold path "are to be developed more or less simultaneously, as far as possible according to the capacity of each individual. They are all linked together and each helps the cultivation of the others." Bhikkhu Bodhi explains that "with a certain degree of progress all eight factors can be present simultaneously, each supporting the others. However, until that point is reached, some sequence in the unfolding of the path is inevitable".
According to the discourses in the Pali and Chinese canons, right view, right resolve, right speech, right action, right livelihood, right effort, and right mindfulness are used as the support and requisite conditions for the practice of right concentration. Understanding of the right view is the preliminary role, and is also the forerunner of the entire Noble Eightfold Path. The practitioner should first try to understand the concepts of right view. Once right view has been understood, it will inspire and encourage the arising of right intention within the practitioner. Right intention will lead to the arising of right speech. Right speech will lead to the arising of right action. Right action will lead to the arising of right livelihood. Right livelihood will lead to the arising of right effort. Right effort will lead to the arising of right mindfulness. The practitioner must make the right effort to abandon the wrong view and to enter into the right view. Right mindfulness is used to constantly remain in the right view. This will help the practitioner restrain greed, hatred and delusion.
Once these support and requisite conditions have been established, a practitioner can then practice right concentration more easily. During the practice of right concentration, one will need to use right effort and right mindfulness to aid concentration practice. In the state of concentration, one will need to investigate and verify his or her understanding of right view. This will then result in the arising of right knowledge, which will eliminate greed, hatred and delusion. The last and final factor to arise is right liberation.
 Wisdom (Prajñā • Paññā)
"Wisdom", sometimes translated as "discernment" at its preparatory role, provides the sense of direction with its conceptual understanding of reality. It is designed to awaken the faculty of penetrative understanding to see things as they really are. At a later stage, when the mind has been refined by training in moral discipline and concentration, and with the gradual arising of right knowledge, it will arrive at a superior right view and right intention.
 Right view
Right view (samyag-dṛṣṭi • sammā-diṭṭhi) can also be translated as "right perspective", "right vision" or "right understanding". It is the right way of looking at life, nature, and the world as they really are. It is to understand how reality works. It acts as the reasoning for someone to start practicing the path. It explains the reasons for human existence, suffering, sickness, aging, death, the existence of greed, hatred, and delusion. It gives direction and efficacy to the other seven path factors. Right view begins with concepts and propositional knowledge, but through the practice of right concentration, it gradually becomes transmuted into wisdom, which can eradicate the fetters of the mind. Understanding of right view will inspire the person to lead a virtuous life in line with right view. In the Pali and Chinese canons, it is explained thus:  
And what is right view? Knowledge with reference to suffering, knowledge with reference to the origination of suffering, knowledge with reference to the cessation of suffering, knowledge with reference to the way of practice leading to the cessation of suffering: This is called right view.
There are two types of right view:
1. View with taints: this view is mundane. Having this type of view will bring merit and will support the favourable existence of the sentient being in the realm of samsara.
2. View without taints: this view is supramundane. It is a factor of the path and will lead the holder of this view toward self-awakening and liberation from the realm of samsara.
Right view has many facets; its elementary form is suitable for lay followers, while the other form, which requires deeper understanding, is suitable for monastics. Usually, it involves understanding the following reality:
1. Moral law of karma: Every action (by way of body, speech, and mind) will have karmic results (a.k.a. reaction). Wholesome and unwholesome actions will produce results and effects that correspond with the nature of that action. It is the right view about the moral process of the world.
2. The three characteristics: everything that arises will cease (impermanence). Mental and body phenomena are impermanent, source of suffering and not-self.
3. Suffering: Birth, aging, sickness, death, sorrow, lamentation, pain, grief, distress, and despair are suffering. Not being able to obtain what one wants is also suffering. The arising of craving is the proximate cause of the arising of suffering and the cessation of craving is the proximate cause of the cessation of the suffering. The quality of ignorance is the root cause of the arising of suffering, and the elimination of this quality is the root cause of the cessation of suffering. The way leading to the cessation of suffering is the noble eightfold path. This type of right view is explained in terms of Four Noble Truths.
Right view for monastics is explained in detail in the Sammādiṭṭhi Sutta ("Right View Discourse"), in which Ven. Sariputta instructs that right view can alternately be attained by the thorough understanding of the unwholesome and the wholesome, the four nutriments, the twelve nidanas or the three taints. "Wrong view" arising from ignorance (avijja), is the precondition for wrong intention, wrong speech, wrong action, wrong livelihood, wrong effort, wrong mindfulness and wrong concentration. The practitioner should use right effort to abandon the wrong view and to enter into right view. Right mindfulness is used to constantly remain in right view.
The purpose of right view is to clear one's path of the majority of confusion, misunderstanding, and deluded thinking. It is a means to gain right understanding of reality. Right view should be held with a flexible, open mind, without clinging to that view as a dogmatic position. In this way, right view becomes a route to liberation rather than an obstacle.
 Right intention
Right intention (samyak-saṃkalpa • sammā sankappa) can also be known as "right thought", "right resolve", "right conception" , "right aspiration" or "the exertion of our own will to change". In this factor, the practitioner should constantly aspire to rid themselves of whatever qualities they know to be wrong and immoral. Correct understanding of right view will help the practitioner to discern the differences between right intention and wrong intention. In the Chinese and Pali Canon, it is explained thus: 
And what is right resolve? Being resolved on renunciation, on freedom from ill will, on harmlessness: This is called right resolve.
It means the renunciation of the worldly things and an accordant greater commitment to the spiritual path; good will; and a commitment to non-violence, or harmlessness, towards other living beings.
 Ethical conduct (Śīla • Sīla)
Main article: Buddhist ethics
For the mind to be unified in concentration, it is necessary to restrain from unwholesome deeds of body and speech to prevent the faculties of bodily action and speech from becoming tools of the defilements. Ethical conduct is used primarily as aids for mental purification.
 Right speech
Right speech (samyag-vāc • sammā-vācā), deals with the way in which a Buddhist practitioner would best make use of their words. In the Pali Canon, it is explained thus:
And what is right speech? Abstaining from lying, from divisive speech, from abusive speech, and from idle chatter: This is called right speech.
The Samaññaphala Sutta, Kevatta Sutta and Cunda Kammaraputta Sutta elaborate:
Abandoning false speech...He speaks the truth, holds to the truth, is firm, reliable, no deceiver of the world...
Abandoning divisive speech...What he has heard here he does not tell there to break those people apart from these people here...Thus reconciling those who have broken apart or cementing those who are united, he loves concord, delights in concord, enjoys concord, speaks things that create concord...
Abandoning abusive speech...He speaks words that are soothing to the ear, that are affectionate, that go to the heart, that are polite, appealing and pleasing to people at large...
Abandoning idle chatter...He speaks in season, speaks what is factual, what is in accordance with the goal, the Dhamma, and the Vinaya. He speaks words worth treasuring, seasonable, reasonable, circumscribed, connected with the goal...
The Abhaya Sutta elaborates:
In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial (or: not connected with the goal), unendearing and disagreeable to others, he does not say them.
In the case of words that the Tathagata knows to be factual, true, unbeneficial, unendearing and disagreeable to others, he does not say them.
In the case of words that the Tathagata knows to be factual, true, beneficial, but unendearing and disagreeable to others, he has a sense of the proper time for saying them.
In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial, but endearing and agreeable to others, he does not say them.
In the case of words that the Tathagata knows to be factual, true, unbeneficial, but endearing and agreeable to others, he does not say them.
In the case of words that the Tathagata knows to be factual, true, beneficial, and endearing and agreeable to others, he has a sense of the proper time for saying them. Why is that? Because the Tathagata has sympathy for living beings.
 Right action
Right action (samyak-karmānta • sammā-kammanta) can also be translated as "right conduct". As such, the practitioner should train oneself to be morally upright in one's activities, not acting in ways that would be corrupt or bring harm to oneself or to others. In the Chinese and Pali Canon, it is explained as: 
And what is right action? Abstaining from taking life, from stealing, and from illicit sex [or sexual misconduct]. This is called right action.
And what, monks, is right action? Abstaining from taking life, abstaining from stealing, abstaining from unchastity: This, monks, is called right action.
For the lay follower, the Cunda Kammaraputta Sutta elaborates:
And how is one made pure in three ways by bodily action? There is the case where a certain person, abandoning the taking of life, abstains from the taking of life. He dwells with his...knife laid down, scrupulous, merciful, compassionate for the welfare of all living beings. Abandoning the taking of what is not given, he abstains from taking what is not given. He does not take, in the manner of a thief, things in a village or a wilderness that belong to others and have not been given by them. Abandoning sensual misconduct, he abstains from sensual misconduct. He does not get sexually involved with those who are protected by their mothers, their fathers, their brothers, their sisters, their relatives, or their Dhamma; those with husbands, those who entail punishments, or even those crowned with flowers by another man. This is how one is made pure in three ways by bodily action.
For the monastic, the Samaññaphala Sutta adds:
Abandoning uncelibacy, he lives a celibate life, aloof, refraining from the sexual act that is the villager's way.
 Right livelihood
Right livelihood (samyag-ājīva • sammā-ājīva). This means that practitioners ought not to engage in trades or occupations which, either directly or indirectly, result in harm for other living beings. In the Chinese and Pali Canon, it is explained thus:
And what is right livelihood? There is the case where a disciple of the noble ones, having abandoned dishonest livelihood, keeps his life going with right livelihood: This is called right livelihood.
The five types of businesses that are harmful to undertake are:
1. Business in weapons: trading in all kinds of weapons and instruments for killing.
2. Business in human beings: slave trading, prostitution, or the buying and selling of children or adults.
3. Business in meat: "meat" refers to the bodies of beings after they are killed. This includes breeding animals for slaughter.
4. Business in intoxicants: manufacturing or selling intoxicating drinks or addictive drugs.
5. Business in poison: producing or trading in any kind of toxic product designed to kill.
 Samādhi: mental discipline, concentration, meditation
Samadhi is literally translated as "concentration", it is achieved through training in the higher consciousness, which brings the calm and collectedness needed to develop true wisdom by direct experience.
 Right effort
Right effort (samyag-vyāyāma • sammā-vāyāma) can also be translated as "right endeavor". In this factor, the practitioners should make a persisting effort to abandon all the wrong and harmful thoughts, words, and deeds. The practitioner should instead be persisting in giving rise to what would be good and useful to themselves and others in their thoughts, words, and deeds, without a thought for the difficulty or weariness involved. In the Chinese and Pali Canon, it is explained thus:
And what, monks, is right effort?
(i) There is the case where a monk generates desire, endeavors, activates persistence, upholds and exerts his intent for the sake of the non-arising of evil, unskillful qualities that have not yet arisen.
(ii) He generates desire, endeavors, activates persistence, upholds and exerts his intent for the sake of the abandonment of evil, unskillful qualities that have arisen.
(iii) He generates desire, endeavors, activates persistence, upholds and exerts his intent for the sake of the arising of skillful qualities that have not yet arisen.
(iv) He generates desire, endeavors, activates persistence, upholds and exerts his intent for the maintenance, non-confusion, increase, plenitude, development, and culmination of skillful qualities that have arisen:
This, monks, is called right effort.
Although the above instruction is given to the male monastic order, it is also meant for the female monastic order and can be practiced by lay followers of both genders.
The above four phases of right effort mean to:
1. Prevent the unwholesome that has not yet arisen in oneself.
2. Let go of the unwholesome that has arisen in oneself.
3. Bring up the wholesome that has not yet arisen in oneself.
4. Maintain the wholesome that has arisen in oneself.
 Right mindfulness
Right mindfulness (samyak-smṛti • sammā-sati), also translated as "right memory", "right awareness" or "right attention". Here, practitioners should constantly keep their minds alert to phenomena that affect the body and mind. They should be mindful and deliberate, making sure not to act or speak due to inattention or forgetfulness. In the Pali Canon, it is explained thus:
And what, monks, is right mindfulness?
(i) There is the case where a monk remains focused on the body in and of itself—ardent, aware, and mindful—putting away greed and distress with reference to the world.
(ii) He remains focused on feelings in and of themselves—ardent, aware, and mindful—putting away greed and distress with reference to the world.
(iii) He remains focused on the mind in and of itself—ardent, aware, and mindful—putting away greed and distress with reference to the world.
(iv) He remains focused on mental qualities in and of themselves—ardent, aware, and mindful—putting away greed and distress with reference to the world.
This, monks, is called right mindfulness.
Although the above instruction is given to the male monastic order, it is also meant for the female monastic order and can be practiced by lay followers from both genders.
Bhikkhu Bodhi, a monk of the Theravada tradition, further explains the concept of mindfulness as follows:
The mind is deliberately kept at the level of bare attention, a detached observation of what is happening within us and around us in the present moment. In the practice of right mindfulness the mind is trained to remain in the present, open, quiet, and alert, contemplating the present event. All judgments and interpretations have to be suspended, or if they occur, just registered and dropped.
The Maha Satipatthana Sutta also teaches that by mindfully observing these phenomena, we begin to discern its arising and subsiding and the Three Characteristics of Dharma in direct experience, which leads to the arising of insight and the qualities of dispassion, non-clinging, and release
 Right concentration
Right concentration (samyak-samādhi • sammā-samādhi), as its Pali and Sanskrit names indicate, is the practice of concentration (samadhi). As such, the practitioner concentrates on an object of attention until reaching full concentration and a state of meditative absorption (jhana). Traditionally, the practice of samadhi can be developed through mindfulness of breathing (anapanasati), through visual objects (kasina), and through repetition of phrases. Samadhi is used to suppress the five hindrances in order to enter into jhana. Jhana is an instrument used for developing wisdom by cultivating insight and using it to examine true nature of phenomena with direct cognition. This leads to cutting off the defilements, realizing the dhamma and, finally, self-awakening. During the practice of right concentration, the practitioner will need to investigate and verify their right view. In the process right knowledge will arise, followed by right liberation. In the Pali Canon, it is explained thus:
And what is right concentration?
(i) Herein a monk aloof from sense desires, aloof from unwholesome thoughts, attains to and abides in the first meditative absorption [jhana], which is detachment-born and accompanied by applied thought, sustained thought, joy, and bliss.
(ii) By allaying applied and sustained thought he attains to, and abides in the second jhana, which is inner tranquillity, which is unification (of the mind), devoid of applied and sustained thought, and which has joy and bliss.
(iii) By detachment from joy he dwells in equanimity, mindful, and with clear comprehension and enjoys bliss in body, and attains to and abides in the third jhana, which the noble ones [ariyas] call "dwelling in equanimity, mindfulness, and bliss".
(iv) By giving up of bliss and suffering, by the disappearance already of joy and sorrow, he attains to, and abides in the fourth jhana, which is neither suffering nor bliss, and which is the purity of equanimity — mindfulness.
This is called right concentration.
Although this instruction is given to the male monastic order, it is also meant for the female monastic order and can be practiced by lay followers from both genders.
According to the Pali and Chinese canon, right concentration is dependent on the development of preceding path factors:
The Blessed One said: "Now what, monks, is noble right concentration with its supports and requisite conditions? Any singleness of mind equipped with these seven factors — right view, right resolve, right speech, right action, right livelihood, right effort, and right mindfulness — is called noble right concentration with its supports and requisite conditions.
 The acquired factors
In the Mahācattārīsaka Sutta which appears in the Chinese and Pali canons, the Buddha explains that cultivation of the noble eightfold path leads to the development of two further factors, which are right knowledge, or insight (sammā-ñāṇa), and right liberation, or release (sammā-vimutti). These two factors fall under the category of wisdom (paññā).
 Right knowledge and right liberation
Right knowledge is seeing things as they really are by direct experience, not as they appear to be, nor as the practitioner wants them to be, but as they truly are. A result of Right Knowledge is the tenth factor - Right liberation
These two factors are the end result of correctly practicing the noble eightfold path, which arise during the practice of right concentration. The first to arise is right knowledge: this is where deep insight into the ultimate reality arises. The last to arise is right liberation: this is where self-awakening occurs and the practitioner has reached the pinnacle of their practice.
 The noble eightfold path and cognitive psychology
In the essay "Buddhism Meets Western Science", Gay Watson explains:
Buddhism has always been concerned with feelings, emotions, sensations, and cognition. The Buddha points both to cognitive and emotional causes of suffering. The emotional cause is desire and its negative opposite, aversion. The cognitive cause is ignorance of the way things truly occur, or of three marks of existence: that all things are unsatisfactory, impermanent, and without essential self.
The noble eightfold path is, from this psychological viewpoint, an attempt to change patterns of thought and behavior. It is for this reason that the first element of the path is right understanding (sammā-diṭṭhi), which is how one's mind views the world. Under the wisdom (paññā) subdivision of the noble eightfold path, this worldview is intimately connected with the second element, right thought (sammā-saṅkappa), which concerns the patterns of thought and intention that controls one's actions. These elements can be seen at work, for example, in the opening verses of the Dhammapada:
All experience is preceded by mind,
Led by mind,
Made by mind.
Speak or act with a corrupted mind,
And suffering follows
As the wagon wheel follows the hoof of the ox.
All experience is preceded by mind,
Led by mind,
Made by mind.
Speak or act with a peaceful mind,
And happiness follows
Like a never-departing shadow.
Audio / Audio Source
Thus, by altering one's distorted worldview, bringing out "tranquil perception" in the place of "perception polluted", one is able to ease suffering. Watson points this out from a psychological standpoint:
Research has shown that repeated action, learning, and memory can actually change the nervous system physically, altering both synaptic strength and connections. Such changes may be brought about by cultivated change in emotion and action; they will, in turn, change subsequent experience.