Animal rights is the philosophy according to which many or all sentient animals have moral worth independent of their utility to humans, and that their most basic interests—such as avoiding suffering—should be afforded the same consideration as similar interests of human beings. The argument from marginal cases is often used to reach this conclusion. This argument holds that if marginal human beings such as infants, senile people, and the cognitively disabled are granted moral status and negative rights, then nonhuman animals must be granted the same moral consideration, since animals do not lack any known morally relevant characteristic that marginal-case humans have.

Broadly speaking, and particularly in popular discourse, the term "animal rights" is often used synonymously with "animal protection" or "animal liberation". More narrowly, "animal rights" refers to the idea that many animals have fundamental rights to be treated with respect as individuals—rights to life, liberty, and freedom from torture—that may not be overridden by considerations of aggregate welfare.

Many animal rights advocates oppose assigning moral value and fundamental protections on the basis of species membership alone. They consider this idea, known as speciesism, a prejudice as irrational as any other, and hold that animals should not be considered property or used as food, clothing, entertainment, or beasts of burden merely because they are not human. Cultural traditions such as Jainism, Taoism, Hinduism, Buddhism, Shinto, and animism also espouse varying forms of animal rights.

In parallel to the debate about moral rights, North American law schools now often teach animal law, and several legal scholars, such as Steven M. Wise and Gary L. Francione, support extending basic legal rights and personhood to nonhuman animals. The animals most often considered in arguments for personhood are hominids. Some animal-rights academics support this because it would break the species barrier, but others oppose it because it predicates moral value on mental complexity rather than sentience alone. As of November 2019^[update], 29 countries had enacted bans on hominoid experimentation; Argentina granted captive orangutans basic human rights in 2014. Outside of primates, animal-rights discussions most often address the status of mammals (compare charismatic megafauna). Other animals (considered less sentient) have gained less attention—insects relatively little (outside Jainism) and animal-like bacteria hardly any. The vast majority of animals have no legally recognised rights.

Critics of animal rights argue that nonhuman animals are unable to enter into a social contract, and thus cannot have rights, a view summarised by the philosopher Roger Scruton, who writes that only humans have duties, and therefore only humans have rights. Another argument, associated with the utilitarian tradition, maintains that animals may be used as resources so long as there is no unnecessary suffering; animals may have some moral standing, but any interests they have may be overridden in cases of comparatively greater gains to aggregate welfare made possible by their use, though what counts as "necessary" suffering or a legitimate sacrifice of interests can vary considerably. Certain forms of animal-rights activism, such as the destruction of fur farms and of animal laboratories by the Animal Liberation Front, have attracted criticism, including from within the animal-rights movement itself, and prompted the U.S. Congress to enact laws, including the Animal Enterprise Terrorism Act, allowing the prosecution of this sort of activity as terrorism.

Serious discussion about animal rights began in the 18th and 19th century Europe, but respect for animals can be found in most cultures and traditions, including Hinduism, Buddhism, Jainism, and some African and Indigenous cultures. In the Western world, Aristotle viewed animals as lacking reason and existing for human use, though other ancient philosophers believed animals deserved gentle treatment.^{[citation needed]} Major religious traditions, chiefly Indian or Dharmic religions, opposed animal cruelty. While scholars like Descartes saw animals as unconscious automata, and Kant denied direct duties to animals, Jeremy Bentham emphasized their capacity to suffer. The publications of Charles Darwin eventually eroded the Cartesian view of animals. Darwin noted the mental and emotional continuity between humans and animals, suggesting the possibility of animal suffering. The anti-vivisection movement emerged in the late 19th and early 20th centuries, driven significantly by women. From the 1970s onward, growing scholarly and activist interest in animal treatment has aimed to raise awareness and reform laws to improve animal rights and human–animal relationships.^{[citation needed]}

For some the basis of animal rights is in religion or animal worship (or in general nature worship), with some religions banning killing any animal. In other religions animals are considered unclean. Hindu and Buddhist societies abandoned animal sacrifice and embraced vegetarianism from the 3rd century BCE. One of the most important sanctions of the Jain, Hindu, and Buddhist faiths is the concept of ahimsa, or refraining from the destruction of life. According to Buddhism, humans do not deserve preferential treatment over other living beings. The Dharmic interpretation of this doctrine prohibits the killing of any living being. These Indian religions' dharmic beliefs are reflected in the ancient Indian works of the Tolkāppiyam and Tirukkural, which contain passages that extend the idea of nonviolence to all living beings.

In Islam, animal rights were recognized early by the Sharia. This recognition is based on both the Qur'an and the Hadith. The Qur'an contains many references to animals, detailing that they have souls, form communities, communicate with God, and worship Him in their own way. Muhammad forbade his followers to harm any animal and asked them to respect animals' rights. Nevertheless, Islam does allow eating of certain species of animals.