Antoine Doinel (Jean-Pierre Léaud) is a twelve year old boy living in Paris. His life is not a happy one. The family is poor. His parents constantly fight; his mother is having an affair. Their attitudes towards their son range from neglect to indifference to scolding. At school, Antoine is always getting into trouble, which leads him to rebel against his strict teachers, which leads to him getting into more trouble.
Antoine's best friend René encourages him to skip school. They play hooky for a day, which only gets Antoine into more trouble when he tells the school that his mother died, but gets caught in the lie. Finally his mother cuts him a break, acting nicer to him and promising him 1000 francs if he does well on an essay he has to write for class—but that only leads to further disaster.
The 400 Blows is commonly regarded as a landmark of the French New Wave. The huge success of the film established Truffaut as one of the leaders of French cinema. It was followed by four more films recounting the life of Antoine Doinel over the next twenty years, all starring Jean-Pierre Leaud, collectively referred to as The Adventures of Antoine Doinel. The other films in the series are considerably Lighter and Softer.
- Abusive Parents: Antoine's, especially his mother. When she first appears, Antoine says good evening to her; she returns this coldly and tersely, and immediately berates him for not buying flour. In general, she sees him as an inconvenience, refers to him as "the kid", does not show him affection, except in front of other adults. She suddenly changes her tune after Antoine has run away from home and briefly becomes warmer towards him. Her husband is only marginally better, and both have become especially cruel to him by the end. In his interview with the psychologist, Antoine reveals more sad details about his antagonistic relationship with his mother, including being sent to a foster mother.
- Amazingly Embarrassing Parents: Particularly cruel version: Once Antoine's parents learn that he's been skipping school, they decide to punish him in the most humiliating him in the worst way imaginable to a preteen boy by going down to school, storming into his classroom, slapping him in front of all his classmates, and letting him (and everyone else in the room) know, in no uncertain terms, that there's more to come once he gets home. They then leave him to stew in terror and suspense for the rest of the school day.
- Armor-Piercing Question: During Antoine's interview with a psychologist, during which he mostly has his usual deadpan demeanour, he is asked if he has ever slept with a girl. The question takes him by surprise, and he grins and hides his face before replying.
- Author Avatar: Little Antoine's story was based off Truffaut's childhood experiences. Further films in the series are fictional.
- Bittersweet Ending: By the end, sweet-natured Antoine is considered a worthless delinquent. His own mother washes her hands of him and requests that after a stint in juvenile detention he be sent to a work camp by the shore where she doesn't have to deal with him anymore. But at least he gets to see the ocean - in one of French cinema's most famous and beautiful scenes.
- "Blind Idiot" Translation: The French title, Les Quatre Cents Coups is a reference to a French idiom, "faire les quatre cents coups", which means "to raise hell". The English title is a completely literal translation, which is nonsensical in context. The original translator tried to give the film the more appropriate name Wild Oats, but the distributor changed it back.
- Buxom Is Better: Discussed in a sarcastic manner by Antoine's stepfather, who says a secretary at his office got promoted through sleeping with the boss. He pronounces her "well-armed" then says "She has the talents for the position" while making the universal 'big breasts' gesture.
- Can't Get Away with Nuthin': Antoine. If he breaks any rule or makes any mischief, he will get punished and suffer Disproportionate Retribution.
- The Cameo: Truffaut put a lot of people he knew in the movie. Jacques Demy is a cop, Phillipe de Broca is at the fair, and the voices of both Jean-Luc Godard and Jean-Paul Belmondo can be heard. Jeanne Moreau is the lady with a dog.
- Clock Tampering: René does this, so that his father leaves earlier than planned.
- Cool and Unusual Punishment: After Antoine accidentally starts a fire at home, his parents "punish" him by taking him to the cinema. They mention that on a previous occasion, they had stuffed him with ice cream.
- Copycat Mockery: A particularly cruel and unusual example: a boy at the centre for juvenile delinquents tells of how when he cried, his father used to imitate him on his violin.
- Creator Cameo: Francois Truffaut can be seen at the fair when Antoine and René are playing hooky. He's riding next to Antoine in the centrifuge.
- Deadpan Snarker:
- His teacher, who says "Doinel was perfectly entitled to write about his grandfather's death, even though he seems to have a habit of killing off his relations", referring to Antoine's lie about his mother being dead.
- The caretaker who catches Antoine returning the typewriter. On the spot, he telephone's Antoine's father, saying "let's say it's a surprise - not a pleasant one".
- Disproportionate Retribution: Much of what happens to Antoine. He's a good-hearted, intelligent, sensitive young man, but prone to mischief and hasn't quite figured out the status quo. But the Disproportionate Retribution escalates until by the end of the film, everyone in his life has written him off as an incurable delinquent. The worst things he does in the movie are cheat on an essay and steal a typewriter. For this he's sent to prison and disowned by his parents.
- Dull Surprise: When Antoine's parents find out that Antoine skipped school, his mother is not surprised at all. When her husband asks why, she simply replies that nothing about her son surprises her. However, the real reason is that she already knew, but could not say anything because she was kissing her affair partner at the time.
- Eiffel Tower Effect: Guess what's in the very first shot? In fact the entire opening credits sequence is a montage of shots of the Tower as filmed from various moving cars.
- Forged Message: After they skip school, Antoine and Rene realise that they need excuse notes for school. Rene has an old one, says he will cut the date off, and he lends it to Antoine to copy in his mother's handwriting. Antoine tries to do this, but accidentally writes "René", and promptly burns the evidence. He ends up going without a note.
- Freeze-Frame Ending: One of if not the most famous example of the trope. As young Antoine finally reaches the coast from his perpetual series of bad luck and federal injustice. He's still being chased, and has nowhere to go beyond the coast, but is enjoying the beach and an innocent sense of freedom, causing him to smile back towards the land and, consequently, into the camera. The camera then freezes and zooms on his face.
- Gratuitous English: One of Truffaut's favorite tropes, here used for a joke with the English teacher at Antoine's school.Teacher: (in English) Where is the girl?
Abbou: The girl has bit.
Teacher: No, bitch.
Teacher: (emphasizing): Beeeeetch.
- The Ken Burns Effect: Used exactly once and to great effect. The famous Freeze-Frame Ending is paired with a zoom in to Antoine's face, quickly going from middle distance (when the image freezes) to tight closeup.
- Limited Wardrobe: Justified. Poor as he was, Antoine wears the same checkered jacket throughout.
- Mama's Baby, Papa's Maybe: Antoine's mother admits that her husband is not Antoine's father.
- Manly Tears: The only time Antoine is seen crying is in the police van as he is taken to prison, and very subtly so: his tears catch the light from the streets of the city.
- Military School: After an incident in which Antoine accidentally starts a fire, his father threatens to send him to the Prytanée military school. After this threat, Antoine does not dare return home when he runs out of school.
- No Ending: Ends with Antoine looking exhausted in a Freeze Frame in the middle of an unresolved chase scene.
- Overly Long Gag: During the literature class, a pupil tears a page out of his exercise book when he makes a mistake. He keeps on doing this throughout the scene, until there are no pages left in the book.
- Playing Games at Work: When Antoine is locked up at the police station for the night, the police officers on duty are seen playing a dice game.
- Plagiarism in Fiction: Antoine makes the foolish decision to plagiarize Balzac for his literature essay. This gets him into a lot of trouble.
- Poor Man's Porn: The boys in Antoine's class pass around a calendar with a drawing of a sexy woman in lingerie. Naturally, Antoine is the one that the teacher catches. Later, he filches a cheesecake picture of some actress posted outside a movie theater.
- The Runaway: Antoine attempts this a number of times, first spending a night at a factory to escape punishment for lying about his mother dying. Later he spends several days hiding out at his friend's house.
- Sadistic Choice: At the juvenile centre, Antoine is accused of starting his meal before being instructed. He is offered the choice of the choice of the left or right hand, which is then used to slap his face.
- Sadist Teacher: "Sourpuss", the literature teacher at Antoine's school. To be fair, Antoine brings troubles on himself, by doing stuff like scribbling on the walls and plagiarizing an essay. But Sourpuss is still a nasty piece of work who takes delight in publicly humiliating Antoine. When Antoine's friend sticks up for him Sourpuss grabs the friend by the neck and physically yanks him out of the classroom, throwing his papers after him.
- Sexy Figure Gesture: The "large bosom" version, used by Antoine's stepfather to describe the secretary in his office. See Buxom Is Better, above.
- Skipping School:
- Antoine and René skip school for a day, because they are afraid of being punished if they arrive late.
- In a short scene, a teacher leads the class running through the streets of Paris, for exercise. When the teacher is not looking, small groups of them run off and hide, until there are almost none left.
- Slice of Life: Simply the story of a troubled but good-hearted young boy.
- The Stool Pigeon: Antoine's classmate Mauricet sees Antoine and René skipping school, and promptly turns up at Antoine's house to ask Antoine's parents if he is better, as he was off school the day before.
- Stupid Crooks: Poor Antoine, when he decides to steal a typewriter from his father's office, with the intention of selling it to make money, even though he and René know that typewriters are all numbered (they are seen discussing this). When they fail to sell the typewriter, Antoine foolishly decides to return it, in a Paper-Thin Disguise of a wide-brimmed hat; and that is when he is caught by the caretaker.
- The Voice: At the juvenile centre, Antoine has a long interview with a female psychologist. The camera remains on Antoine the whole time, and the psychologist is only heard, and not seen.