Published in 1975, Animal Liberation has been cited as a formative influence on leaders of the modern animal liberation movement.
The central argument of the book is an expansion of the utilitarian concept that "the greatest good of the greatest number" is the only measure of good or ethical behaviour, and Singer believes that there is no reason not to apply this principle to other animals, arguing that the boundary between human and "animal" is completely arbitrary.
There are far more differences between a great ape and an oyster, for example, than between a human and a great ape, and yet the former two are lumped together as "animals", whereas we are considered "human" in a way that supposedly differentiates us from all other "animals."

He popularised the term "speciesism", which had been coined by English writer Richard D. Ryder to describe the practice of privileging humans over other animals, and therefore argues in favour of the equal consideration of interests of all sentient beings.
In Animal Liberation, Singer argues in favour of veganism and against animal experimentation.
Singer describes himself as a flexible vegan.
He writes, "That is, I'm vegan when it's not too difficult to be vegan, but I'm not rigid about this, if I'm traveling for example."

In an article for the online publication Chinadialogue, Singer called Western-style meat production cruel, unhealthy, and damaging to the ecosystem.
He rejected the idea that the method was necessary to meet the population's increasing demand, explaining that animals in factory farms have to eat food grown explicitly for them, and they burn up most of the food's energy just to breathe and keep their bodies warm.
In a 2010 Guardian article he titled, "Fish: the forgotten victims on our plate," Singer drew attention to the welfare of fish.
He quoted (author) Alison Mood's startling statistics from a report she wrote, which was released on fishcount.org.uk just a month before the Guardian article.
Singer states that she "has put together what may well be the first-ever systematic estimate of the size of the annual global capture of wild fish.
It is, she calculates, in the order of one trillon, although it could be as high as 2.7tn."

Some chapters of Animal Liberation are dedicated to criticising testing on animals but, unlike groups such as PETA, Singer is willing to accept such testing when there is a clear benefit for medicine.
In November 2006, Singer appeared on the BBC programme Monkeys, Rats and Me: Animal Testing and said that he felt that Tipu Aziz's experiments on monkeys for research into treating Parkinson's disease could be justified.
Whereas Singer has continued since the publication of Animal Liberation to promote vegetarianism and veganism, he has been much less vocal in recent years on the subject of animal experimentation.

Singer has defended some of the actions of the Animal Liberation Front, such as the stealing of footage from Dr. Thomas Gennarelli's laboratory in May 1984 (as shown in the documentary Unnecessary Fuss), but he has condemned other actions such as the use of explosives by some animal-rights activists and sees the freeing of captive animals as largely futile when they are easily replaced.
Published in 1975, Animal Liberation has been cited as a formative influence on leaders of the modern animal liberation movement. The central argument of the book is an expansion of the utilitarian concept that "the greatest good of the greatest number" is the only measure of good or ethical behaviour, and Singer believes that there is no reason not to apply this principle to other animals, arguing that the boundary between human and "animal" is completely arbitrary. There are far more differences between a great ape and an oyster, for example, than between a human and a great ape, and yet the former two are lumped together as "animals", whereas we are considered "human" in a way that supposedly differentiates us from all other "animals."
He popularised the term "speciesism", which had been coined by English writer Richard D. Ryder to describe the practice of privileging humans over other animals, and therefore argues in favour of the equal consideration of interests of all sentient beings. In Animal Liberation, Singer argues in favour of veganism and against animal experimentation. Singer describes himself as a flexible vegan. He writes, "That is, I'm vegan when it's not too difficult to be vegan, but I'm not rigid about this, if I'm traveling for example."
In an article for the online publication Chinadialogue, Singer called Western-style meat production cruel, unhealthy, and damaging to the ecosystem. He rejected the idea that the method was necessary to meet the population's increasing demand, explaining that animals in factory farms have to eat food grown explicitly for them, and they burn up most of the food's energy just to breathe and keep their bodies warm. In a 2010 Guardian article he titled, "Fish: the forgotten victims on our plate," Singer drew attention to the welfare of fish. He quoted (author) Alison Mood's startling statistics from a report she wrote, which was released on fishcount.org.uk just a month before the Guardian article. Singer states that she "has put together what may well be the first-ever systematic estimate of the size of the annual global capture of wild fish. It is, she calculates, in the order of one trillon, although it could be as high as 2.7tn."
Some chapters of Animal Liberation are dedicated to criticising testing on animals but, unlike groups such as PETA, Singer is willing to accept such testing when there is a clear benefit for medicine. In November 2006, Singer appeared on the BBC programme Monkeys, Rats and Me: Animal Testing and said that he felt that Tipu Aziz's experiments on monkeys for research into treating Parkinson's disease could be justified. Whereas Singer has continued since the publication of Animal Liberation to promote vegetarianism and veganism, he has been much less vocal in recent years on the subject of animal experimentation.
Singer has defended some of the actions of the Animal Liberation Front, such as the stealing of footage from Dr. Thomas Gennarelli's laboratory in May 1984 (as shown in the documentary Unnecessary Fuss), but he has condemned other actions such as the use of explosives by some animal-rights activists and sees the freeing of captive animals as largely futile when they are easily replaced.
Peter Singer