The Buddha taught that because of karma, beings are bound to the ever-turning wheel of rebirth. Only when a person stops believing in the existence of a permanent and real self can he or she become free from karma. Bhikkhu Bodhi, Jan Chozen Bays, and Jeffrey Hopkins discuss what that means.

What is karma, according to the Buddhist teachings?

Bhikkhu Bodhi: Perhaps we could begin with the description of the Buddha’s enlightenment experience as given in various sutras in the Middle Length Discourses of the Buddha (Pali, Majjhima Nikaya). This gives a very concise statement of the early Buddha’s understanding of karma. The Buddha’s enlightenment unfolded by way of what are called the Three Higher Knowledges. The first of these is the Buddha’s knowledge of his past lives—recollecting his previous lives going back hundreds of thousands of eons. The second is his knowledge of the death and rebirth of beings, which involves understanding how beings transmigrate according to their karma. Perhaps I could read a passage describing this from the Bhayabherava Sutta:
“When my concentrated mind was purified, bright and so on, I directed it to knowledge of the passing away and rebirth of beings. With the divine eye, which is purified and surpasses the human, I saw beings passing away and being reborn, inferior and superior, bare and ugly, fortunate and unfortunate. I understood how beings pass on according to their actions thus: “These beings who are ill-conducted in body, speech and mind, revilers of noble ones, wrong in their views, giving effect to wrong view in their actions, with the breakup of the body after death, have reappeared in the plane of misery, in a bad destination, in the lower worlds, even in hell. “But these worthy beings who were well conducted in body, speech and mind, not revilers of noble ones, right in their views, giving effect to right view in their actions, on the breakup of the body after death, have been reborn in a good destination, even in the heavenly world. “Thus, with the divine eye I saw beings passing away and being reborn and I understood how beings pass on according to their actions.”
Finally, the third knowledge is described as the knowledge of the Four Noble Truths. But preceding that comes the understanding of the chain of dependent origination (Pali, patichcha-samuppada), or dependent arising. This involves understanding the dynamics of how karma, in conjunction with the basic defilements of ignorance and craving, brings about rebirth. Jan Chozen Bays: As a physician, I teach karma from a scientific point of view, because what I love about karma is that it is rational. Karma is like the laws of physics. It’s almost mathematically precise, and there is a great relief in that. Because if you understand karma, you really understand who and what you are, and you understand the rest of the universe too, because the laws of karma are universally applicable. When I teach about rebirth, I ask people to consider what happens to the physical elements of the body after they die. I ask them, if we buried you in the ground with no preservatives and dug you up in a week, would we recognize you? Yes. If we dug you up in a year, would we recognize you? Maybe. If we dug you up in ten years, would we recognize you? No. So what happened to the elements that made up the body? They all dispersed and became other things.
If you die angry, what happens to that energy of anger?
Appreciating this, people begin to understand that on the physical level there is a endless chain of energy that passes through a series of changes. Then if you apply the same principle to our mental and emotional energy, you can also ask where it goes. That energy is also not destroyed, though the energy that was “you” will transform. Karma is a wonderfully exact force in our lives. If you die angry, what happens to that energy of anger? Where does it go? When you walk into a room where people have been angry, you can sense it—the energy is palpable. So is that the kind of energy you would like to pass on, to be picked up by other lives? One can also look back at what energies have been passed down to you—perhaps by your family or the people who influenced you—and that helps you understand that energy doesn’t die but rather continues on in some form. I don’t worry too much about questions like, “Am I going to remember that I was Queen Victoria or her servant?” People get caught up in that sort of approach to karma and rebirth, but it’s almost irrelevant. The continuity of the energy is what’s important. What do you want to pass on—suffering or happiness? Bhikkhu Bodhi: Somebody who is a strict materialist might reply to your argument by saying that of course the mental energy is dependent on the physical basis—the body, the nervous system, the brain—and so when the body dies whatever mental energy has been generated by that person perishes also. In response to that, I would look at two extreme cases: an extreme case of evil, Adolph Hitler, and on the other hand, somebody like Mother Theresa, who engaged in so much self-sacrificing labor for the good of others. If we take a materialistic viewpoint, then when each of them dies, it is the complete end. Maybe for Hitler there are a few moments of remorse or regret, then it’s just blank, it’s all over. When Mother Theresa is about to die, there might be a few moments of rejoicing for her altruistic work, then everything is over. If one takes the materialistic viewpoint, then, it means that the universe has no underlying principle of moral justice. However, if we are going to recognize some kind of moral justice in the universe, there would have to be some continuity beyond death. That could take the form of an eternal afterlife in one realm or another—eternity in hell, eternity in heaven—but that seems difficult to reconcile with the position that any kind of volitional action generates only a finite mental force. What seems more convincing is that our various activities in this life will produce rebirth in a realm where they will expend their force over a finite period of time, to be followed by a new existence somewhere else. Jeffrey Hopkins: The appeal of karma to me is psychological, based on my own experience of attitudes and actions from earlier parts of my life that I have seen play out later. I meet a lot of people who have an experiential sense of karma. We even see it on television and in the movies. On the last episode of Seinfeld, the characters paid for their karma. They all ended up in jail for very specific things they had done that they were reflecting on. The movie Flatliners was very successful, and it was all about karma. Things people had done earlier in a lifetime were coming back to haunt them. As each moment of consciousness perishes, it passes its entire accumulated storage of impressions, experiences, potentially memories, and karmic deposits on to the succeeding moment of consciousness.At another level, understanding emptiness enhances one’s understanding of karma. Proper understanding of emptiness should not yield the view that things do not exist, that actions and so forth do not exist. A proper understanding of emptiness requires a proper understanding of dependent arising. Once there is dependent arising, there is cause and effect. Once there is cause and effect, our actions have effect. And since the mind is something that is not physical, it can serve as a repository of the potencies established by actions and can carry them from lifetime to lifetime. If a person’s seeming understanding of emptiness undercuts the entire existence of phenomena, the traditions that I know hold this to be wrong. If one thoroughly understands actions and their effects, the very fact that an action can create an effect means that it does not exist in and of itself. So, understanding dependent arising leads to understanding emptiness. In turn, understanding emptiness leads to greater understanding of the cause and effect of actions.