The definition
"Intention, I tell you, is kamma. Intending, one does kamma by way of body, speech, & intellect."
-- AN VI.63

Taking responsibility for one's actions
"'I am the owner of my actions (kamma), heir to my actions, born of my actions, related through my actions, and have my actions as my arbitrator. Whatever I do, for good or for evil, to that will I fall heir'...
"[This is a fact that] one should reflect on often, whether one is a woman or a man, lay or ordained...
"Now, based on what line of reasoning should one often reflect... that 'I am the owner of my actions (kamma), heir to my actions, born of my actions, related through my actions, and have my actions as my arbitrator. Whatever I do, for good or for evil, to that will I fall heir'? There are beings who conduct themselves in a bad way in body... in speech... and in mind. But when they often reflect on that fact, that bad conduct in body, speech, and mind will either be entirely abandoned or grow weaker...
"A disciple of the noble ones considers this: 'I am not the only one who is owner of my actions, heir to my actions, born of my actions, related through my actions, and have my actions as my arbitrator; who -- whatever I do, for good or for evil, to that will I fall heir. To the extent that there are beings -- past and future, passing away and re-arising -- all beings are the owner of their actions, heir to their actions, born of their actions, related through their actions, and live dependent on their actions. Whatever they do, for good or for evil, to that will they fall heir.' When he/she often reflects on this, the [factors of the] path take birth. He/she sticks with that path, develops it, cultivates it. As he/she sticks with that path, develops it and cultivates it, the fetters are abandoned, the obsessions destroyed."
-- AN V.57

Kamma should be known and understood
"'Kamma should be known. The cause by which kamma comes into play should be known. The diversity in kamma should be known. The result of kamma should be known. The cessation of kamma should be known. The path of practice for the cessation of kamma should be known.' Thus it has been said. In reference to what was it said?
"Intention, I tell you, is kamma. Intending, one does kamma by way of body, speech, & intellect.
"And what is the cause by which kamma comes into play? Contact is the cause by which kamma comes into play.
"And what is the diversity in kamma? There is kamma to be experienced in hell, kamma to be experienced in the realm of common animals, kamma to be experienced in the realm of the hungry shades, kamma to be experienced in the human world, kamma to be experienced in the world of the devas. This is called the diversity in kamma.
"And what is the result of kamma? The result of kamma is of three sorts, I tell you: that which arises right here & now, that which arises later [in this lifetime], and that which arises following that. This is called the result of kamma.
"And what is the cessation of kamma? From the cessation of contact is the cessation of kamma; and just this noble eightfold path -- right view, right resolve, right speech, right action, right livelihood, right effort, right mindfulness, right concentration -- is the path of practice leading to the cessation of kamma.
"Now when a disciple of the noble ones discerns kamma in this way, the cause by which kamma comes into play in this way, the diversity of kamma in this way, the result of kamma in this way, the cessation of kamma in this way, & the path of practice leading to the cessation of kamma in this way, then he discerns this penetrative holy life as the cessation of kamma.
"'Kamma should be known. The cause by which kamma comes into play... The diversity in kamma... The result of kamma... The cessation of kamma... The path of practice for the cessation of kamma should be known.' Thus it has been said, and in reference to this was it said."
-- AN VI.63

Reflecting on one's actions (The Buddha teaches his young son)
[The Buddha:] "How do you construe this, Rahula: What is a mirror for?"
[Rahula:] "For reflection, sir."
[The Buddha:] "In the same way, Rahula, bodily acts, verbal acts, and mental acts are to be done with repeated reflection.
"Whenever you want to perform a bodily act, you should reflect on it: 'This bodily act I want to perform -- would it lead to self-affliction, to the affliction of others, or to both? Is it an unskillful bodily act, with painful consequences, painful results?' If, on reflection, you know that it would lead to self-affliction, to the affliction of others, or to both; it would be an unskillful bodily act with painful consequences, painful results, then any bodily act of that sort is absolutely unfit for you to do. But if on reflection you know that it would not cause affliction... it would be a skillful bodily action with happy consequences, happy results, then any bodily act of that sort is fit for you to do.
"While you are performing a bodily act, you should reflect on it: 'This bodily act I am doing -- is it leading to self-affliction, to the affliction of others, or to both? Is it an unskillful bodily act, with painful consequences, painful results?' If, on reflection, you know that it is leading to self-affliction, to affliction of others, or both... you should give it up. But if on reflection you know that it is not... you may continue with it.
"Having performed a bodily act, you should reflect on it... If, on reflection, you know that it led to self-affliction, to the affliction of others, or to both; it was an unskillful bodily act with painful consequences, painful results, then you should confess it, reveal it, lay it open to the Teacher or to a knowledgeable companion in the holy life. Having confessed it... you should exercise restraint in the future. But if on reflection you know that it did not lead to affliction... it was a skillful bodily action with happy consequences, happy results, then you should stay mentally refreshed and joyful, training day and night in skillful mental qualities.
...[similarly for verbal and mental acts]...
"Rahula, all the priests and contemplatives in the course of the past who purified their bodily acts, verbal acts, and mental acts, did it through repeated reflection on their bodily acts, verbal acts, and mental acts in just this way.
"All the priests and contemplatives in the course of the future... All the priests and contemplatives at present who purify their bodily acts, verbal acts, and mental acts, do it through repeated reflection on their bodily acts, verbal acts, and mental acts in just this way.
"Therefore, Rahula, you should train yourself: 'I will purify my bodily acts through repeated reflection. I will purify my verbal acts through repeated reflection. I will purify my mental acts through repeated reflection.' Thus you should train yourself."
-- MN 61

Five pleasant things to be gained by acting skillfully
"These five things are welcome, agreeable, pleasant, and hard to obtain in the world. Which five? Long life... beauty... pleasure... status... rebirth in heaven... Now, I tell you, these five things are not to be obtained by reason of prayers or wishes. If they were to be obtained by reason of prayers or wishes, who here would lack them? It's not fitting for the disciple of the noble ones who desires long life to pray for it or to delight in doing so. Instead, the disciple of the noble ones who desires long life should follow the path of practice leading to long life. In so doing, he will attain long life, either human or divine...(Similarly with beauty, pleasure, status, and rebirth in heaven)..."
-- AN V.43

The most noble kamma of all: the ending of kamma
"Monks, these four types of kamma have been directly realized, verified, & made known by me. Which four? There is kamma that is dark with dark result. There is kamma that is bright with bright result. There is kamma that is dark & bright with dark & bright result. There is kamma that is neither dark nor bright with neither dark nor bright result, leading to the ending of kamma.
"And what is kamma that is dark with dark result? There is the case where a certain person fabricates an injurious bodily fabrication, fabricates an injurious verbal fabrication, fabricates an injurious mental fabrication. Having fabricated an injurious bodily fabrication, having fabricated an injurious verbal fabrication, having fabricated an injurious mental fabrication, he rearises in an injurious world. On rearising in an injurious world, he is there touched by injurious contacts. Touched by injurious contacts, he experiences feelings that are exclusively painful, like those of the beings in hell. This is called kamma that is dark with dark result.
"And what is kamma that is bright with bright result? There is the case where a certain person fabricates a non-injurious bodily fabrication ... a non-injurious verbal fabrication ... a non-injurious mental fabrication ... He rearises in a non-injurious world ... There he is touched by non-injurious contacts ... He experiences feelings that are exclusively pleasant, like those of the Ever-radiant Devas. This is called kamma that is bright with bright result.
"And what is kamma that is dark & bright with dark & bright result? There is the case where a certain person fabricates a bodily fabrication that is injurious & non-injurious ... a verbal fabrication that is injurious & non-injurious ... a mental fabrication that is injurious & non-injurious ... He rearises in an injurious & non-injurious world ... There he is touched by injurious & non-injurious contacts ... He experiences injurious & non-injurious feelings, pleasure mingled with pain, like those of human beings, some devas, and some beings in the lower realms. This is called kamma that is dark & bright with dark & bright result.
"And what is kamma that is neither dark nor bright with neither dark nor bright result, leading to the ending of kamma? right view, right resolve, right speech, right action, right livelihood, right effort, right mindfulness, right concentration. This is called kamma that is neither dark nor bright with neither dark nor bright result, leading to the ending of kamma."
-- AN IV.235