The Witches is a children's fantasy horror novel by the British writer Roald Dahl. It was published in 1983 by Jonathan Cape in London, with illustrations by Quentin Blake (like many of Dahl's works). The story is set partly in Norway and partly in the United Kingdom, and features the experiences of a young British boy and his Norwegian grandmother in a world where child-hating evil witches secretly exist.

A seven-year-old British boy called Lucas goes to live with his Norwegian grandmother after his parents are killed in a car crash. The grandmother is a wonderful story teller. He loves all the stories, but he is enthralled by the one about witches, which she says are horrific creatures who seek to kill human children. She tells the boy that she knows of five children who were cursed by witches and tells him how to recognize them.

She also tells about witchophiles, men and women who hunt witches. When Lucas asks his grandmother if she is one, she says yes, albeit retired, then tells of an incident which cost the grandmother her left thumb and which is so horrible she cannot bear to speak of it. Other than that, she admits her witch hunting career was a failure, as she never came close to tracking the Grand High Witch. (a witchophile who kills the Grand High Witch would be akin to a soldier winning the Medal of Honor). While witches look and act like human women, they are actually "demons in human shape." They have bald heads, clawed hands, blue spit, large nostrils (but only slightly larger than human women), and square, toeless feet. To conceal their appearance, they wear wigs to hide their baldness and gloves to hide their claws. Hiding their feet are the toughest part, as human girls prefer to wear pointy-toed pumps or high heels, the witches must follow suit, which is extremely painful for their square feet. Witches also detect children by "stink waves", which are projected conversely to when a child bathes, an unwashed child would project very weak waves, whereas a child that just got out of the bath would project a pungent odor to witches. When a child matures into an adult, the stink waves disappear. The boy thinks this is good as he never has to take another bath, but the grandmother limits it to once a week.

As specified in the parents' will, Lucas and his grandmother have to return to England, where he was born and was in school, and where the house he is inheriting is located. Lucas's grandmother warns Lucas to be on his guard, however, since English witches are known to be among the cruelest in the world. They are particularly notorious for turning children into loathsome creatures so that unsuspecting adults kill them.

As Lucas asks more questions, Grandmother reveals that witches in different countries have different customs; and that while the witches in each country have close affiliations with one another, they are not allowed to communicate with witches from other countries. She warns him to beware of the Grand High Witch, the feared and diabolical leader of all of the world's witches, who each year visits their councils in every country.

Shortly after arriving back in England, while Lucas is working on the roof of the tree-house he has been building, he sees a strange woman in black staring up at him with an eerie smile, and he realizes that she is a witch. When the witch offers him a snake to entice him, he climbs further up the tree and stays there, not daring to come down until his grandmother comes looking for him. This persuades Lucas and his grandmother to be especially wary; and he carefully scrutinizes all women to determine whether or not they might be witches. However, she also warns that he must be discretionary "You can't go around yanking the hair of every woman you see, even if she is wearing gloves".

When the grandmother becomes ill with pneumonia, the doctor orders her to cancel a planned holiday in Norway. Instead, they go to a luxury hotel in Bournemouth on England's south coast, where Lucas gets into trouble with the manager after his new pet mice scare one of the chambermaids. Under threat of having the poor creatures drowned in a bucket if they are found out of their cage, the boy goes to train his pet mice in the hotel ballroom when the members of the fictional "Royal Society for the Prevention of Cruelty to Children" show up for their annual meeting. The boy quickly realizes that this is really the yearly gathering of England's witches when one of them reaches underneath her hair to scratch at her scalp with a gloved hand, but is trapped in the room before he can escape.

A young woman goes on stage and removes her entire face, which is really a mask, and turns around to reveal a truly hideous visage revealing herself to be the Grand High Witch. She immediately reveals her displeasure at the English witches failure to eliminate enough children and demands that they exterminate the lot of them before the next meeting. When one witch dares to protest the sheer impossibility of such a task, the Grand High Witch responds by using fiery jets from her eyes to "frizzle her like a fritter". After this warning, the Grand High Witch unveils a master plan. All of England's witches are to purchase sweet shops (with "homemade" money printed from her money-making machine) and give away free sweets and chocolates for the grand opening laced with her latest creation, "Formula 86 delayed-action mouse-maker", a magic potion meant to turn the drinker into a mouse at a specific time with a single drop. The intent is that the children's teachers can kill the transformed children for them.

To demonstrate, the Grand High Witch turns a gluttonous child named Bruno Jenkins (who is lured to the convention hall by the promise of free chocolate) into a mouse. Shortly after, the witches smell the narrator's presence and corner him. The Grand High Witch then pours an entire bottle of Formula 86 down the narrator's throat, instantly turning him into a mouse.

The transformed child retains his sentience, personality and even his voice. After tracking down Bruno, the transformed boy returns to his grandmother's hotel room and tells her what he has learned. He suggests turning the tables on the witches by slipping the potion into their food. He also remembers that when the Grand High Witch gave her instructions how to make the formula, she also said she would give away some ready-made formula to elderly witches, as some of the recipe (such as climbing trees to get the eggs of a gruntle) were likely too strenuous for such old women. With some difficulty, he manages to get his hands on a bottle of the potion from the Grand High Witch's room.

After an attempt to return Bruno to his parents fails spectacularly, mainly due to Mrs. Jenkins's fear of mice, the grandmother takes Bruno and the narrator to the dining hall, then he sneaks towards the kitchen, holding the potion. He spies the witches coming in to dinner on his way and finally enters the kitchen successfully, where he pours the potion into the green pea soup intended for the witches' dinner. On the way back from the kitchen, a cook spots the narrator and chops off part of his tail with a carving knife, before he manages to escape back to his grandmother. At the dinner, the witches all start shrinking and realize, too late, that they are transforming into mice. The hotel staff and the guests all panic and unknowingly, the staff end up killing the Grand High Witch and all of England's witches. Since he is a mouse, the grandmother figures England's compulsory school attendance laws no longer apply to him, and says they are free to return to Norway, which pleases the grandson. This is actually overheard by the taxi driver on the ride away from the hotel, who by chance is an admirer of rodents and remarks that if her grandson is a mouse, she should "expect some great-grandchildren in a few weeks".

Having returned home, the boy and his grandmother then devise a plan to get rid of the world of witches. Learning the recipe for Mouse Maker and the location of the Grand High Witch's Norwegian castle, they will travel there and use the potion to change her successor and assistants into mice, then release cats to destroy them before they escape. Using the Grand High Witch's money-making machine and information on all the other witches in various countries, they will then try to track down and eradicate them all over the world. The grandmother also reveals that, as a mouse, the boy will probably only live about another nine years. However, he accepts his fate, not wishing to outlive his beloved grandmother.

The book was adapted into an unabridged audio reading by Lynn Redgrave (ISBN 0-060-53616-0), a stage play and a two-part radio dramatization for the BBC, a 1990 movie directed by Nicolas Roeg which starred Angelica Huston and Rowan Atkinson, and an opera by Marcus Pius and Ole Pius.

Another movie adaptation was directed in 2020 by Robert Zemeckis, which starred Anne Hathaway, Octavia Spencer, and Stanley Tucci. The setting of the movie was set in the USA like the 1996 movie adaptation of Matilda, only it takes place in Demopolis, Alabama. The witches no longer have purple tinges in their eyes, but they were given elongated mouths and sharp teeth instead.