Law of Karma in Buddhism is defined as the law of moral causation. Karma means an action or doing or whatever one thinks or does. The theory regarding the law of Karma is considered as a fundamental doctrine in Buddhism. This belief of karma was dominant in India much before the advent of Buddha. Yet, it was Lord Buddha who defined and devised this doctrine of karma in the complete form in which it is available today. In Buddhism, karma is used for defining those actions that spring from the objective of a human being. In Buddhist philosophy, law of karma is not imposed from without, but is worked into our very nature. The formation of mental habits, the increasing proneness to evil, the hardening influence of repetition which undermines the effective freedom of the self are comprehended under the law of karma. Buddhist philosophy states that one cannot escape from the effects of their acts. The past in a real sense produces the present and the future. The law of karma is the principle working out justice in human relations.

According to the Law of Karma, it is through a difference in their karma that men are not all alike but some are long lived, some short lived, some healthy, and some sickly, etc. This explanation makes the enjoyer courteous, for he must do good again to deserve it. This law of Karma insists on individual responsibility and the reality of a future life. It recognises that the retribution of sin depends on the status of the sinner. If a man weak in mind and morals does an evil deed, it may lead him to the hell. If a good man does it he may escape with a small pain in this life. It is as if a man were to put a lump of salt into a small cup of water, the water would be made salt and undrinkable. But if the same lump of salt were put into the Ganga River, the water of the Ganges would not be perceptibly tainted. The theory of karma is much older than Buddhism, though it gets a logical justification in the philosophy of becoming. Men are considered as temporary links in a long chain of causes and effects where no link is independent of the rest. The history of an individual does not begin at his birth, but has been for ages in the making.

Further, Buddhist philosophy also states that when karma becomes the supreme principle superior to gods and men, it is difficult to assign any place to the initiative and endeavour of man. If everything that happens is determined by it, it is hard to see why the individual should take thought of what he does. He cannot but act in harmony with the law. Salvation is another name for acquiescence in the course of things. Karma, according to Buddhism, is not a mechanical principle, but is organic in character. The self grows and expands. There is no self, but only an evolving consciousness which may be spread out in a series of states. Though the present is determined by the past, the future remains open and depends on the direction of one`s will. The willpower of the present by the past is not, however, a merely mechanical one. The law of karma tells that there is continuity between the past and the present and that the present accords with the past. However, this does not mean that the present is the only possible outcome of the past.

As per the theories in Buddhism, when a person attains the highest condition, it is said that karma has no effect. All the past deeds with their results vanish for ever. The condition of freedom is past good and evil. It is also believed that morality ceases to be of otherworldly worth when moral acts are looked upon as an obstruction to final bliss, in so far as they inevitably bring about a reward and maintain the round of existence. All moral conduct is a preparation for the final state. When the ideal is realised the struggle ceases. It is the Upanishad doctrine that whatever the individual who has attained liberation does, he does without attachment. It is not deeds in themselves that bring about results, but deeds springing from selfish desires. It is often said that the highest condition is therefore above moral rules and the operation of the law of karma, yet morality has an organic bearing on the end. Throughout life there are changes. Birth and death are vital changes. Buddhism does not explain the means by which the stability of karma is maintained between two lives separated by the phenomenon of death. Buddhism says that Law of Karma keeps going the life process and when it is exhausted the existence of an individual terminates.