Though the origins of the concept of ahimsa are unknown, the earliest references to ahimsa are found in the texts of historical Vedic religion, dated to 8th century BCE. Here, ahimsa initially relates to "non-injury" without a moral connotation, but later to non-violence to animals and then, to all beings. The idea emerges again in the Hindu texts Mahabharata and Manu Smriti, where ahimsa is said to be merited by good Karma. Though meat-eating and slaughter of animals are criticized by some Hindu texts, other texts present counter-arguments in support of hunting and ritual sacrifice. In the 19th and 20th centuries, prominent figures of Indian spirituality such as Swami Vivekananda, Ramana Maharishi, Swami Sivananda and A.C. Bhaktivedanta Swami emphasized the importance of ahimsa. Mohandas Karamchand Gandhi applied ahimsa to politics, by his non-violent satyagrahas.
Ahimsa in Jainism emphasizes vegetarianism and bans hunting and ritual sacrifice. Jains go out of their way so as not to hurt even small insects and other minuscule animals and make considerable efforts not to injure plants in everyday life as far as possible. In accordance to this policy, eating of some foods, whose cultivation harms small insects and worms as well as agriculture itself, is to be abstained from. Violence in self-defense, criminal law, and war are accepted by Hindus and Jains. Though ahimsa is not used as a technical term in Buddhism unlike the other two religions, it condemns ritual sacrifice and war and moral codes emphasize the importance of not taking life.
Some source texts discuss meat eating as a fact without referring to the ethical side of the issue. The Dharmasutra law books written around the 5th or 4th century BCE contain regulations for meat eating and lists of edible animals. Medical treatises of the Ayurveda discuss and recommend meat from a purely health-related viewpoint without even mentioning the aspect of ahimsa. Examples are the Sushruta Samhita written in the 3rd or 4th century CE, which recommends beef for certain patients and for pregnant women, and the Charaka Samhita which describes meat as superior to all other kinds of food for convalescents.
Several highly authoritative scriptures bar violence against domestic animals except in the case of ritual sacrifice. This view is clearly expressed in the Mahabharata, the Bhagavata Purana (11.5.13-14), and the Chandogya Upanishad (8.15.1). It is also reflected in the Manu Smriti (5.27-44), a particularly renowned traditional Hindu lawbook (Dharmaśāstra). These texts strongly condemn the slaughter of animals and meat eating. The Mahabharata permits hunting by warriors (Kshatriyas), but opposes it in the case of hermits who must be strictly non-violent.
Nevertheless the sources show that this compromise between supporters of ahimsa and meat eaters was shaky and hotly disputed. Even the loopholes – ritual slaughter and hunting – were challenged by advocates of ahimsa. The Mahabharata and the Manu Smriti (5.27-55) contain lengthy discussions about the legitimacy of ritual slaughter. In the Mahabharata both sides present various arguments to substantiate their viewpoints. Moreover, a hunter defends his profession in a long discourse.
Most of the arguments proposed in favour of non-violence to animals refer to rewards it entails before or after death and to horrible karmic consequences of violence. In particular, it is pointed out that he who deliberately kills an animal will on his part be eaten by an animal in a future existence due to karmic retribution. Ahimsa is described as a prerequisite for acquiring supernatural faculties, highest bliss and ultimate salvation; moreover it is said to protect against all kinds of dangers. The Manu Smriti (10.63), Kautilya’s Arthashastra (1.3.13) and the Vasishtha Dharmasutra (4.4) point out that ahimsa is a duty for all the four classes (Varnas) of society. The texts declare that ahimsa should be extended to all forms of life. They also give attention to the protection of plants. The Manu Smriti prohibits wanton destruction of both wild and cultivated plants (11.145). Hermits (Sannyasins) had to live on a fruitarian diet so as to avoid the destruction of plants.
Under these circumstances the defenders of hunting and ritual slaughter had to deny the violent nature of these activities. They asserted that lawful violence is in fact non-violence; according to them sacrificial killing is not killing, but is meant for the welfare of the whole world. They also suggested that such killing is in fact a benevolent act, because the slaughtered animal will attain a high rebirth in the cycle of reincarnation. Moreover they argued that some species have been created for the purpose of being sacrificed and eaten by humans, that it is normal for animals to kill and eat other animals, that agriculture, too, inevitably leads to the death of many animals, that plants are living beings as well and must still be destroyed, that we unintentionally and unknowingly destroy life forms all the time, and that a hunted animal has a fair chance to survive by killing the hunter.
According to some interpretations, the concept of ahimsa as expounded in the scriptures and law books is not meant to imply pacifism; war is seen as a normal part of life and the natural duty of the warriors. In the second chapter of the Bhagavad Gita Krishna refutes the pacifist ideas of Arjuna and uses various arguments to convince him that he must fight and kill in the impending battle. According to this interpretation of the scriptures, face-to-face combat is highly meritorious and fighters who die in battle go to heaven. This interpretation, however, is not authoritative and directly contradicts the high value placed upon ahimsa in the vast majority of the Hindu tradition and by its greatest saints. This more widely accepted view is well represented by Mahatma Gandhi, who made clear throughout his life and his own commentary on the Gita that it was "an allegory in which the battlefield is the soul and Arjuna, man's higher impulses struggling against evil.
Mohandas Karamchand Gandhi promoted the principle of ahimsa very successfully by applying it to all spheres of life, particularly to politics. His non-violent resistance movement satyagraha had an immense impact on India, impressed public opinion in Western countries and influenced the leaders of various civil rights movements such as Martin Luther King Jr. In Gandhi’s thought ahimsa precludes not only the act of inflicting a physical injury, but also mental states like evil thoughts and hatred, unkind behavior such as harsh words, dishonesty and lying, all of which he saw as manifestations of violence incompatible with ahimsa. Sri Aurobindo criticized the Gandhian concept of ahimsa as unrealistic and not universally applicable; he adopted a pragmatic non-pacifist position, saying that the justification of violence depends on the specific circumstances of the given situation.
A thorough historical and philosophical study of ahimsa was instrumental in the shaping of Albert Schweitzer's principle of "reverence for life". Schweitzer criticized Indian philosophical and religious traditions for having conceived ahimsa as the negative principle of avoiding violence instead of emphasizing the importance of positive action (helping injured beings).
In Jainism the understanding and implementation of ahimsa is more radical, scrupulous, and comprehensive than in any other religion. Non-violence is seen as the most essential religious duty for everyone (a statement often inscribed on Jain temples). Like in Hinduism, the aim is to prevent the accumulation of harmful Karma. When Mahavira revived and reorganized the Jain movement in the 6th or 5th century BCE, ahimsa was already an established, strictly observed rule. Parshva, the earliest Jain leader (Tirthankar) whom modern Western historians consider to be a historical figure, lived in about the 8th century BCE. He founded the community to which Mahavira’s parents belonged. Ahimsa was already part of the "Fourfold Restraint" (Caujjama), the vows taken by Parshva’s followers. In the times of Mahavira and in the following centuries Jains were at odds with both Buddhists and followers of the Vedic religion or Hindus, whom they accused of negligence and inconsistency in the implementation of ahimsa. There is some evidence, however, that ancient Jain ascetics accepted meat as alms if the animal had not been specifically killed for them. Modern Jains deny this vehemently, especially with regard to Mahavira himself. According to the Jain tradition either lacto-vegetarianism or veganism is mandatory.
The Jain concept of ahimsa is characterized by several aspects. It does not make any exception for ritual sacrificers and professional warrior-hunters. Killing of animals for food is absolutely ruled out. Jains also make considerable efforts not to injure plants in everyday life as far as possible. Though they admit that plants must be destroyed for the sake of food, they accept such violence only inasmuch as it is indispensable for human survival, and there are special instructions for preventing unnecessary violence against plants. Jains go out of their way so as not to hurt even small insects and other minuscule animals. In their view injury caused by carelessness is like injury caused by deliberate action. Eating honey is strictly outlawed, as it would amount to violence against the bees. Some Jains abstain from farming because it inevitably entails unintentional killing or injuring of many small animals, such as worms and insects, but agriculture is not forbidden in general and there are Jain farmers.
In contrast, Jains agree with Hindus that violence in self-defense can be justified, and they agree that a soldier who kills enemies in combat is performing a legitimate duty. Jain communities accepted the use of military power for their defense, and there were Jain monarchs, military commanders, and soldiers.
Though, theoretically, all life forms are said to deserve full protection from all kinds of injury, Jains admit that this ideal cannot be completely implemented in practice. Hence, they recognize a hierarchy of life. Mobile beings are given higher protection than immobile ones. For the mobile beings they distinguish between one-sensed, two-sensed, three-sensed, four-sensed and five-sensed ones; a one-sensed animal has touch as its only sensory modality. The more senses a being has, the more they care about its protection. Among the five-sensed beings, the rational ones (humans) are most strongly protected by Jain ahimsa. In the practice of ahimsa the requirements are less strict for the lay persons who have undertaken anuvrata (Lesser Vows) than for the monks and nuns who are bound by mahavrata (Great Vows).
Since the beginnings of the Buddhist community, monks and nuns have had to commit themselves to the Ten Precepts of moral conduct. In ancient Buddhism, lay persons were encouraged, but not obliged, to commit themselves to observe the Five Precepts of morality (). In both codes the first rule is to abstain from taking the life of a sentient being ().
Unlike the Vedic religion, ancient Buddhism had strong misgivings about violent ways of punishing criminals and about war. Both were not explicitly condemned, but peaceful ways of conflict resolution and punishment with the least amount of injury were encouraged.