The animal rights movement, sometimes called the animal liberation, animal personhood, or animal advocacy movement, is a social movement that advocates an end to the rigid moral and legal distinction drawn between human and non-human animals, an end to the status of animals as property, and an end to their use in the research, food, clothing, and entertainment industries. The argument from marginal cases is often used in animal rights advocacy which asserts that if certain humans with limited cognitive capacities are granted moral consideration, then non-human animals, who may possess different forms of intelligence or sentience, should also be afforded similar negative rights and moral consideration.

All animal liberationists believe that the individual interests of non-human animals deserve recognition and protection, but the movement can be split into two broad camps. Animal rights advocates believe that these basic interests confer moral rights of some kind on the animals, and/or ought to confer legal rights on them; see, for example, the work of Tom Regan. Utilitarian liberationists, on the other hand, do not believe that animals possess moral rights, but argue, on utilitarian grounds — utilitarianism in its simplest form advocating that we base moral decisions on the greatest happiness of the greatest number — that, because animals have the ability to suffer, their suffering must be taken into account in any moral philosophy. To exclude animals from that consideration, they argue, is a form of discrimination that they call speciesism; see, for example, the work of Peter Singer.

Despite these differences, the terms "animal liberation" and "animal rights" are generally used interchangeably. Factional division has also been characterized as that between the reformist or mainstream faction and the radical abolitionist and direct action factions. The mainstream faction is largely professionalized and focuses on soliciting donations and gaining media representation. Actors in the reformist movement believe that humans should stop abusing animals. They employ activities that include moral shocks. It has been noted that the power of the animal rights movement in the United States is centralized in professionalized nonprofit organizations that aim to improve animal welfare.

The abolitionist faction believes that humans should stop using animals altogether. Gary Francione, a leader in abolitionism, formed his approach in response to the traditional movement's focus on policy reform. Some members of the abolitionist faction view policy reform as counterproductive and rely only on nonviolent education and moral persuasion in their activities. They see the promotion of veganism as a means of creating an antispeciesist culture and abolishing animal agriculture. Other abolitionists believe that animal advocates shouldn't rely only on the promotion of veganism and should use a social movement strategy focused on expressing political claims, like what do all the NGOs participating in the World Day for the End of Speciesism during which they express the claim that speciesist practices have to be banned. This political strategy based on the sociology of the social construction of problems is defended by the activist Anoushavan Sarukhanyan who wrote several articles on the issue. In addition to this theoretical disagreement regarding the strategy to be used by abolitionists, there is also a disagreement regarding the question of direct action. Some argue that direct action was used by all social movements so the animal rights movement should do the same, while others point out that these actions are perceived as violent by the public (because of the media framing) and therefore citizens feel less emotional connection with animal activists and in consequence less support the cause. The action repertory of the abolitionists who use direct action includes property damage, animal releases, intimidation, and sometimes even direct violence, aiming to change society through force. Despite this, the unorganized group of abolitionists who use direct action the most, the Animal Liberation Front (ALF), insists that all the direct actions they do to save animals shouldn't harm any human or animal. Nevertheless, many animal rights actors reject this faction, pointing to the fact that even if the actions of the ALF weren't violent they are still perceived as violent by the public and therefore represent a counterproductive tactic that invites repression (e.g., the Animal Enterprise Terrorism Act) while not necessarily economically or politically challenging the existent systems. There are also abolitionist groups focused around faith-based animal rights theory whose approach is characterized by more spirituality and the idea that we shouldn't harm other creatures unnecessarily. The animal rights movement includes also veganarchists, whose approach is characterized by a critique of capitalism on the grounds that it has led to mass nonhuman, human, and environmental exploitation. Such diversity, researchers have pointed out, is common to social movements and plays a role in sustaining their health.

The modern animal rights movement traces back to the animal protection movement in Victorian England, which was initiated by crusaders in response to the poor treatment of urban workhorses, the conditions under which they were exported for slaughter and their use, along with stray cats and dogs, for vivisection. Public awareness was raised by, for example, Anna Sewell's 1877 novel Black Beauty and by the pioneer Ada Cole who fought for humane conditions for horses destined for slaughter. Other early influences include: Upton Sinclair's 1906 novel The Jungle, which drew attention to slaughterhouse operations; Henry Stephens Salt's treatises on nonhuman animal rights, which drew from human abolitionist arguments for recognizing the personhood of people considered to be property; and the short-lived Fruitlands agrarian commune, which required its residents to eat a vegan diet.

The contemporary movement is regarded as having been founded in the UK in the early 1970s by a group of Oxford university post-graduate philosophy students, now known as the "Oxford Group". The group was led by Rosalind and Stanley Godlovitch, graduate students of philosophy who had recently become vegetarians. The Godlovitches met John Harris and David Wood, also philosophy graduates, who were soon persuaded of the arguments in favour of animal rights and themselves became vegetarian. The group began to actively raise the issue with pre-eminent Oxford moral philosophers, including Professor Richard Hare, both personally and in lectures. Their approach was based not on sentimentality ("kindness to dumb animals"), but on the moral rights of animals. They soon developed (and borrowed) a range of powerful arguments in support of their views, so that Oxford clinical psychologist Richard Ryder, who was shortly to become part of the group, writes that "rarely has a cause been so rationally argued and so intellectually well armed."

It was a 1965 article by novelist Brigid Brophy in The Sunday Times which was pivotal in helping to spark the movement. Brophy wrote:

The relationship of Homo sapiens to the other animals is one of unremitting exploitation. We employ their work; we eat and wear them. We exploit them to serve our superstitions: whereas we used to sacrifice them to our gods and tear out their entrails in order to foresee the future, we now sacrifice them to science, and experiment on their entrail in the hope—or on the mere offchance—that we might thereby see a little more clearly into the present.