user-1: Where is the Noble Eightfold Path found in the Pali Canon?  Are there significant differences among the traditions in its interpretation?

user92: 1. What is the Noble Eightfold Path?
The Noble Eightfold Path is the prescription, made known by the Buddha, for emotional suffering, distress & dissatisfaction.

The Buddha: 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. That is the ancient path, the ancient road, traveled by the Rightly Self-awakened Ones of former times. 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. I followed that path. Following it, I came to direct knowledge of birth... becoming... clinging... craving... feeling... contact... the six sense media... name-&-form... consciousness, direct knowledge of the origination of consciousness, direct knowledge of the cessation of consciousness, direct knowledge of the path leading to the cessation of consciousness. I followed that path.
-SN 12.65, Nagara-suttaṃ 

(For details about what constitutes the path see the reference provided in the next answer.)
2. Where is the Noble Eightfold Path found in the Pali Canon?
It is described in many places throughout the Canon but one detailed example is the Discourse on the Dissection of the Path (SN 45.8, Maggavibhaṅga-suttaṃ).
3. Are there significant differences among the traditions in its interpretation?
No, but as a related side-note, the path culminates with two additional stages, Right Knowledge & Right Release, making it tenfold, as is stated in MN 78, Samaṇamuṇḍika-suttaṃ:

Now, an individual endowed with which ten qualities is one whom I describe as being consummate in what is skillful, foremost in what is skillful, an invincible contemplative attained to the highest attainments? One endowed with the right view of one beyond training, the right resolve of one beyond training, the right speech... the right action... the right livelihood... the right effort... the right mindfulness... the right concentration... the right knowledge... the right release of one beyond training. An individual endowed with these ten qualities is one whom I describe as being consummate in what is skillful, foremost in what is skillful, an invincible contemplative attained to the highest attainments.


user70: According to Magga-vibhanga Sutta: An Analysis of the Path
Now what, is the Noble Eightfold Path? 

Right view

Knowledge with regard to stress, knowledge with regard to the origination of stress, knowledge with regard to the stopping of stress, knowledge with regard to the way of practice leading to the stopping of stress

Right resolve

Being resolved on renunciation, on freedom from ill will, on harmlessness

Right speech

Abstaining from lying, abstaining from divisive speech, abstaining from abusive speech, abstaining from idle chatter

Right action

Abstaining from taking life, abstaining from stealing, abstaining from unchastity

Right livelihood

There is the case where a disciple of the noble ones, having abandoned dishonest livelihood, keeps his life going with right livelihood

Right effort

(i) There is the case where a monk generates desire, endeavors, activates persistence, upholds & 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 & exerts his intent for the sake of the abandonment of evil, unskillful qualities that have arisen.
(iii)He generates desire, endeavors, activates persistence, upholds & 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 & exerts his intent for the maintenance, non-confusion, increase, plenitude, development, & culmination of skillful qualities that have arisen

Right mindfulness

(i) There is the case where a monk remains focused on the body in & of itself — ardent, aware, & mindful — putting away greed & distress with reference to the world.
(ii) He remains focused on feelings in & of themselves — ardent, aware, & mindful — putting away greed & distress with reference to the world. 
(iii) He remains focused on the mind in & of itself — ardent, aware, & mindful — putting away greed & distress with reference to the world. 
(iv) He remains focused on mental qualities in & of themselves — ardent, aware, & mindful — putting away greed & distress with reference to the world.

Right concentration

(i) There is the case where a monk — quite withdrawn from sensuality, withdrawn from unskillful (mental) qualities — enters & remains in the first jhana: rapture & pleasure born from withdrawal, accompanied by directed thought & evaluation. 
(ii) With the stilling of directed thoughts & evaluations, he enters & remains in the second jhana: rapture & pleasure born of concentration, unification of awareness free from directed thought & evaluation — internal assurance.
(iii) With the fading of rapture, he remains equanimous, mindful, & alert, and senses pleasure with the body. He enters & remains in the third jhana, of which the Noble Ones declare, 'Equanimous & mindful, he has a pleasant abiding.' 
(iv) With the abandoning of pleasure & pain — as with the earlier disappearance of elation & distress — he enters & remains in the fourth jhana: purity of equanimity & mindfulness, neither pleasure nor pain.



user-1: The way I explain The Path to non-Buddhists is:
The Noble Eightfold Path

Right View (The Four Noble Truths)
Right Intention

Renunciation: 
Resistance to desire
Goodwill: 
Resistance to anger and aversion
Harmlessness: 
Compassion, 
Don't think or act cruelly, violently or aggressively

Right Speech

Tell the truth
Don't gossip
Don't use offensive or hurtful language

Right Action (The Precepts)

Don't harm other living beings
Don't take things not freely given
Don't engage in sexual misconduct
Don't engage in false speech
Don't abuse drugs or alcohol

Right Livelihood
Don't work in a job that violates The Precepts
Right Effort

Create, preserve and increase healthy states
Prevent, eliminate or decrease harmful states

Right Mindfulness

See things clearly
The Four Foundations of Mindfulness
Be mindful of:

body
feeling
state of mind
phenomena      


Right Concentration

Meditation
Concentration on healthy thoughts and actions



-1: <p>Where is the Noble Eightfold Path found in the Pali Canon?  Are there significant differences among the traditions in its interpretation?</p>
 92: <h2>1. What is the Noble Eightfold Path?</h2>

<p>The <a href="http://en.wikipedia.org/wiki/Noble_Eightfold_Path" rel="nofollow">Noble Eightfold Path</a> is the prescription, made known by the <em>Buddha</em>, for emotional suffering, distress &amp; dissatisfaction.</p>

<blockquote>
  <p><em>The Buddha</em>: 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? <strong>Just this noble eightfold path: right view, right aspiration, right speech, right action, right livelihood, right effort, right mindfulness, right concentration.</strong> That is the ancient path, the ancient road, traveled by the Rightly Self-awakened Ones of former times. I followed that path. Following it, I came to direct knowledge of aging &amp; death, direct knowledge of the origination of aging &amp; death, direct knowledge of the cessation of aging &amp; death, direct knowledge of the path leading to the cessation of aging &amp; death. I followed that path. Following it, I came to direct knowledge of birth... becoming... clinging... craving... feeling... contact... the six sense media... name-&amp;-form... consciousness, direct knowledge of the origination of consciousness, direct knowledge of the cessation of consciousness, direct knowledge of the path leading to the cessation of consciousness. I followed that path.<br>
  <em>-<a href="http://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.065.than.html" rel="nofollow">SN 12.65, Nagara-suttaṃ</a></em>  </p>
</blockquote>

<p><sup>(For details about what constitutes the path see the reference provided in the next answer.)</sup></p>

<h2>2. Where is the Noble Eightfold Path found in the Pali Canon?</h2>

<p>It is described in many places throughout the <a href="http://en.wikipedia.org/wiki/P%C4%81li_Canon" rel="nofollow">Canon</a> but one detailed example is the <em><a href="http://www.accesstoinsight.org/tipitaka/sn/sn45/sn45.008.than.html" rel="nofollow">Discourse on the Dissection of the Path</a> (SN 45.8, Maggavibhaṅga-suttaṃ)</em>.</p>

<h2>3. Are there significant differences among the traditions in its interpretation?</h2>

<p>No, but as a related side-note, the path culminates with two additional stages, Right Knowledge &amp; Right Release, making it tenfold, as is stated in <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.078.than.html" rel="nofollow"><em>MN 78, Samaṇamuṇḍika-suttaṃ</em></a>:</p>

<blockquote>
  <p>Now, an individual endowed with which ten qualities is one whom I describe as being consummate in what is skillful, foremost in what is skillful, an invincible contemplative attained to the highest attainments? One endowed with the right view of one beyond training, the right resolve of one beyond training, the right speech... the right action... the right livelihood... the right effort... the right mindfulness... the right concentration... the right knowledge... the right release of one beyond training. An individual endowed with these ten qualities is one whom I describe as being consummate in what is skillful, foremost in what is skillful, an invincible contemplative attained to the highest attainments.</p>
</blockquote>
 70: <p>According to <a href="http://www.accesstoinsight.org/tipitaka/sn/sn45/sn45.008.than.html" rel="nofollow">Magga-vibhanga Sutta: An Analysis of the Path</a></p>

<p>Now what, is the Noble Eightfold Path? </p>

<ol>
<li><p>Right view</p>

<blockquote>
  <p>Knowledge with regard to stress, knowledge with regard to the origination of stress, knowledge with regard to the stopping of stress, knowledge with regard to the way of practice leading to the stopping of stress</p>
</blockquote></li>
<li><p>Right resolve</p>

<blockquote>
  <p>Being resolved on renunciation, on freedom from ill will, on harmlessness</p>
</blockquote></li>
<li><p>Right speech</p>

<blockquote>
  <p>Abstaining from lying, abstaining from divisive speech, abstaining from abusive speech, abstaining from idle chatter</p>
</blockquote></li>
<li><p>Right action</p>

<blockquote>
  <p>Abstaining from taking life, abstaining from stealing, abstaining from unchastity</p>
</blockquote></li>
<li><p>Right livelihood</p>

<blockquote>
  <p>There is the case where a disciple of the noble ones, having abandoned dishonest livelihood, keeps his life going with right livelihood</p>
</blockquote></li>
<li><p>Right effort</p>

<blockquote>
  <p>(i) There is the case where a monk generates desire, endeavors, activates persistence, upholds &amp; exerts his intent for the sake of the non-arising of evil, unskillful qualities that have not yet arisen.</p>
  
  <p>(ii)He generates desire, endeavors, activates persistence, upholds &amp; exerts his intent for the sake of the abandonment of evil, unskillful qualities that have arisen.</p>
  
  <p>(iii)He generates desire, endeavors, activates persistence, upholds &amp; exerts his intent for the sake of the arising of skillful qualities that have not yet arisen. </p>
  
  <p>(iv)He generates desire, endeavors, activates persistence, upholds &amp; exerts his intent for the maintenance, non-confusion, increase, plenitude, development, &amp; culmination of skillful qualities that have arisen</p>
</blockquote></li>
<li><p>Right mindfulness</p>

<blockquote>
  <p>(i) There is the case where a monk remains focused on the body in &amp; of itself — ardent, aware, &amp; mindful — putting away greed &amp; distress with reference to the world.</p>
  
  <p>(ii) He remains focused on feelings in &amp; of themselves — ardent, aware, &amp; mindful — putting away greed &amp; distress with reference to the world. </p>
  
  <p>(iii) He remains focused on the mind in &amp; of itself — ardent, aware, &amp; mindful — putting away greed &amp; distress with reference to the world. </p>
  
  <p>(iv) He remains focused on mental qualities in &amp; of themselves — ardent, aware, &amp; mindful — putting away greed &amp; distress with reference to the world.</p>
</blockquote></li>
<li><p>Right concentration</p>

<blockquote>
  <p>(i) There is the case where a monk — quite withdrawn from sensuality, withdrawn from unskillful (mental) qualities — enters &amp; remains in the first jhana: rapture &amp; pleasure born from withdrawal, accompanied by directed thought &amp; evaluation. </p>
  
  <p>(ii) With the stilling of directed thoughts &amp; evaluations, he enters &amp; remains in the second jhana: rapture &amp; pleasure born of concentration, unification of awareness free from directed thought &amp; evaluation — internal assurance.</p>
  
  <p>(iii) With the fading of rapture, he remains equanimous, mindful, &amp; alert, and senses pleasure with the body. He enters &amp; remains in the third jhana, of which the Noble Ones declare, 'Equanimous &amp; mindful, he has a pleasant abiding.' </p>
  
  <p>(iv) With the abandoning of pleasure &amp; pain — as with the earlier disappearance of elation &amp; distress — he enters &amp; remains in the fourth jhana: purity of equanimity &amp; mindfulness, neither pleasure nor pain.</p>
</blockquote></li>
</ol>
 -1: <p>The way I explain The Path to non-Buddhists is:</p>

<p><strong>The Noble Eightfold Path</strong></p>

<ol>
<li><p>Right View (The Four Noble Truths)</p></li>
<li><p>Right Intention</p>

<ul>
<li>Renunciation: 
Resistance to desire</li>
<li>Goodwill: 
Resistance to anger and aversion</li>
<li>Harmlessness: 
Compassion, 
Don't think or act cruelly, violently or aggressively</li>
</ul></li>
<li><p>Right Speech</p>

<ul>
<li>Tell the truth</li>
<li>Don't gossip</li>
<li>Don't use offensive or hurtful language</li>
</ul></li>
<li><p>Right Action (The Precepts)</p>

<ul>
<li>Don't harm other living beings</li>
<li>Don't take things not freely given</li>
<li>Don't engage in sexual misconduct</li>
<li>Don't engage in false speech</li>
<li>Don't abuse drugs or alcohol</li>
</ul></li>
<li><p>Right Livelihood
Don't work in a job that violates The Precepts</p></li>
<li><p>Right Effort</p>

<ul>
<li>Create, preserve and increase healthy states</li>
<li>Prevent, eliminate or decrease harmful states</li>
</ul></li>
<li><p>Right Mindfulness</p>

<ul>
<li>See things clearly</li>
<li>The Four Foundations of Mindfulness<br>
Be mindful of:
<ul>
<li>body</li>
<li>feeling</li>
<li>state of mind</li>
<li>phenomena      </li>
</ul></li>
</ul></li>
<li><p>Right Concentration</p>

<ul>
<li>Meditation</li>
<li>Concentration on healthy thoughts and actions</li>
</ul></li>
</ol>
