Richard D. Ryder in the context of Warneford Hospital

Speciesism (/ˈspiːʃiːˌzɪzəm, -siːˌzɪz-/) is a term used in philosophy regarding the treatment of individuals of different species. The term has several different definitions. Some specifically define speciesism as discrimination or unjustified treatment based on an individual's species membership, while others define it as differential treatment without regard to whether the treatment is justified or not. Richard D. Ryder, who coined the term, defined it as "a prejudice or attitude of bias in favour of the interests of members of one's own species and against those of members of other species". Speciesism results in the belief that humans have the right to use non-human animals in exploitative ways which is pervasive in the modern society. Studies from 2015 and 2019 suggest that people who support animal exploitation also tend to have intersectional bias that encapsulates and endorses racist, sexist, and other prejudicial views, which furthers the beliefs in human supremacy and group dominance to justify systems of inequality and oppression.

As a term, speciesism first appeared during a protest against animal experimentation in 1970. Philosophers and animal rights advocates state that speciesism plays a role in the animal–industrial complex, including in the practice of factory farming, animal slaughter, blood sports (such as bullfighting, cockfighting and rodeos), the taking of animals' fur and skin, and experimentation on animals, as well as the refusal to help animals suffering in the wild due to natural processes, and the categorization of certain animals as alien, non-naturalized, feral and invasive giving then the justification to their killing or culling based on these classifications.

Animal Liberation: A New Ethics for Our Treatment of Animals is a 1975 book by the Australian philosopher Peter Singer. It is widely considered within the animal liberation movement to be the founding philosophical statement of its ideas. Singer himself rejected the use of the theoretical framework of rights when it comes to human and nonhuman animals. Following Jeremy Bentham, Singer argued that the interests of animals should be considered because of their ability to experience suffering and that the idea of rights was not necessary in order to consider them. He popularized the term "speciesism" in the book, which had been coined by Richard D. Ryder to describe the exploitative treatment of animals.

A revised edition, Animal Liberation Now, was released in 2023.