Animal Farm begins on Manor Farm in England. After Mr. Jones, the neglectful owner of the farm, has drunkenly shut the animals away and gone to sleep, the animals all assemble in the barn to hear a respected boar named Old Major speak. Old Major proceeds to share his dream of a world without men, one ruled by animals. He points out that all of the suffering endured by the animals is the result of man. Mr. Jones forces the animals to work too hard and then steals the products of their labor. Furthermore, the animals all know that Mr. Jones does not value their lives and will mercilessly slaughter each and every one of them once they have outlived their usefulness. Old Major tells the animals that their lives would be much better if they could overthrow man and find freedom. He cautions them, however, that if they should ever overthrow their human masters, they must take precautions against acting like humans themselves and should remember to treat all animals as equals.

Three days later, Old Major dies and the animals begin to prepare for the rebellion. The preparations are led by the pigs, who are the cleverest animals on the farm. Two pigs in particular—Snowball and Napoleon—take on leadership roles and are aided by Squealer, an extremely persuasive pig. The pigs turn Old Major’s speech into a philosophy, which they call “Animalism.” They then hold weekly meetings to teach the rest of the animals about Animalism, though they find the animals are easily distracted by Moses, a raven who likes to tell the animals about a place called Sugarcandy Mountain where animals go when they die. The rebellion comes sooner than expected when Mr. Jones forgets to feed the animals and then attacks them when he sees them helping themselves. Incensed, the animals drive Mr. Jones and his men off the farm and take over, changing the name to Animal Farm. The pigs paint the principles of Animalism on the barn wall. There are seven commandments in total, and each one comes from Old Major’s speech to the animals.

1. Whatever goes upon two legs is an enemy.

2. Whatever goes upon four legs, or has wings, is a friend.

3. No animal shall wear clothes.

4. No animal shall sleep in a bed.

5. No animal shall drink alcohol.

6. No animal shall kill any other animal.

7. All animals are equal.

The animals are eager to prove themselves a success and complete the harvest more quickly and efficiently than their former human master could ever have done. Most of the animals believe strongly in Animalism and work very hard to do their part for the farm. However, there are troubling indicators that not all the animals are being treated equally. The pigs, being the cleverest of the animals, quickly become the permanent leaders of the farm. Despite the fact that they supervise the farm work instead of performing any labor themselves, the pigs begin claiming extra rations in the form of milk and apples. This seemingly unequal treatment is easily explained away by Squealer, who warns the animals that Mr. Jones might return if the pigs are not given what they need to run the farm successfully. Soon after, Mr. Jones really does return in an effort to recapture the farm. Snowball has been studying military tactics and successfully commands the animals to victory in what the animals later call the “Battle of Cowshed.”

As time goes by, the pigs remain in a leadership position, though the other animals still vote to approve or reject the resolutions submitted by the pigs during weekly Sunday meetings. A power struggle begins to emerge between Snowball and Napoleon, who disagree on nearly everything. While Snowball is an enthusiastic and persuasive orator, Napoleon is better at gaining support behind the scenes. Snowball tries to engage the animals by organizing them into committees and teaching them to read, while Napoleon focuses on the education of the youth, taking nine newborn puppies up to a loft to be personally educated by himself. Snowball and Napoleon’s greatest disagreement is over Snowball’s plan for a windmill. Snowball argues that the windmill would generate electricity that could then be used to heat the animals’ stalls and make their workload lighter. Napoleon argues that the animals will starve if they neglect their farming to focus on a windmill. Though the farm is initially divided, by the time the animals are preparing to cast their final votes, it is clear that Snowball’s passionate speech in favor of the windmill has won them over. Just before the vote, however, Napoleon gives a signal and nine ferocious dogs (the now grown-up puppies) attack Snowball and chase him off the farm. Napoleon addresses the shocked animals and announces that the Sunday meetings are abolished. Farm policy will now be decided by a committee of pigs, over whom he will preside. In an about-face, Napoleon soon announces that they will begin construction on the windmill. Squealer tells the animals that it was originally Napoleon’s idea—Snowball, he says, stole it.

After Napoleon takes power, the quality of life on the farm begins to deteriorate. Building the windmill is grueling work, and the animals are given fewer and fewer rations. When Napoleon announces that he will begin conducting business with the neighboring human farms, the animals are uneasy, but they are convinced by Squealer that there was never an actual rule against trade. The pigs move in to the farmhouse and justify their actions by rewriting the commandment against sleeping in a bed to read “No animals shall sleep in a bed with sheets,” though they convince the rest of the farm that it always said that. The pigs lead a smear campaign against Snowball, who they claim was a criminal working to secretly undermine the farm. Bad events on the farm are routinely attributed to Snowball’s machinations, and when the half-constructed windmill is destroyed in a windstorm, Napoleon is quick to blame the absent pig.

The animals begin the difficult work of rebuilding the windmill, though they are now nearly starving. The hens begin a small rebellion when Napoleon tries to sell their eggs, but they are soon defeated. In the spring, Napoleon calls a meeting in which multiple animals come forward and publicly confess to various crimes. They are immediately executed by Napoleon’s dogs. Disturbed and frightened, the animals look for the commandment against killing animals but find that it now reads “No animal shall kill any other animals without cause.” Meanwhile, Napoleon takes great pains to conceal the failure of the farm from the neighboring humans and begins negotiating a deal to sell some timber to either Mr. Frederick or Mr. Pilkington. After using Mr. Pilkington to drive up the price, Napoleon sells to Mr. Frederick. He is outraged, however, to discover that Mr. Frederick paid him with fake banknotes. The next morning, Mr. Frederick and his men attack the farm and blow up the windmill. Soon after, the pigs discover a case of whiskey in the farmhouse, and the commandment “No animal shall drink alcohol” is secretly changed to “No animal shall drink alcohol to excess.”

As the animals work to rebuild the windmill for the third time, no animal works harder than Boxer, a loyal horse. Though Boxer is nearing retirement age, he does not slow down, wanting to contribute what he can before he retires. Meanwhile, the preferential treatment the pigs grant themselves only grows more obvious. Piglets are discouraged from playing with other young animals, and it is decreed that any animals meeting a pig on a path must step aside. Though the animals remain tired and hungry, Squealer continually announces that the farm is more productive and successful than ever. As the animals no longer clearly remember what life was like under Mr. Jones, they have no way of disputing the pigs’ claims that things are now better. One day, Boxer collapses while working on the windmill. The pigs tell the animals that they are sending Boxer to an animal hospital, but Benjamin, a donkey, sees that the van taking Boxer away is labeled “Horse Slaughterer and Glue Boiler.” Horrified, the animals rush after the van but are unable to free Boxer. Three days later, the pigs announce that Boxer died at the hospital. They shut down the “rumors” about the van by explaining that the veterinarian had recently purchased it and not yet repainted the outside.

As the years pass, many of the animals on the farm grow old and die; there are only a few left who remember the days before the rebellion. Though the animals’ lives are hard, they still take pride in being an animal-run farm. One day, however, the animals are shocked to see that the pigs have learned to walk on two legs. When they return to the barn, a couple of the older animals notice that the wall where the commandments once were now just reads “ALL ANIMALS ARE EQUAL BUT SOME ANIMALS ARE MORE EQUAL THAN OTHERS.” As the weeks pass, the pigs continue to walk on two legs and even begin wearing human clothes that they find in the farmhouse. A week later, Napoleon invites several humans, including Mr. Pilkington, to visit the farm. The men tour the farm and commend Napoleon for making the animals work so hard for so little food. Later that night, the animals watch through a farmhouse window as the pigs play cards with the men. Napoleon gets up and announces that Animal Farm will be reverting to its “correct and original” name, Manor Farm. As the animals look through the window, they suddenly realize that they can no longer tell the difference between the men and the pigs.