Knock-Knock Jokes
The knock-knock joke is one of the most recognizable joke formats in the English language. It follows a rigid call-and-response structure: "Knock knock" / "Who's there?" / [Name] / "[Name] who?" / [Punchline]. The format has been around since at least the 1930s and remains a staple of children's humor and groan-worthy wordplay.
The Appeal of the Format
Knock-knock jokes work because the rigid structure creates a very specific expectation, and the punchline is almost always a pun built on the "who" response. The audience participates by asking the scripted questions, which makes the joke interactive — a feature that's especially appealing to children who are still learning how humor and language work. The format also teaches kids about timing and delivery in a structured way.
Knock knock.
Who's there?
Lettuce.
Lettuce who?
Lettuce in, it's cold out here!
Knock knock.
Who's there?
Boo.
Boo who?
Don't cry, it's just a joke!
Knock knock.
Who's there?
Atch.
Atch who?
Bless you!
Knock knock.
Who's there?
Nobel.
Nobel who?
Nobel, that's why I knocked!
Knock knock.
Who's there?
Tank.
Tank who?
You're welcome!
Knock knock.
Who's there?
Cow says.
Cow says who?
No, a cow says mooooo!
Knock knock.
Who's there?
Interrupting cow.
Interrupting cow wh— MOOO!
Knock knock.
Who's there?
Broken pencil.
Broken pencil who?
Never mind, it's pointless.
Variations and Subversions
Some of the best knock-knock jokes work by breaking the format itself. The "interrupting cow" joke, for example, violates the expected structure by having the punchline arrive before the audience finishes their line. This is a form of benign violation — the rules of the joke are broken, but in a harmless and surprising way. For the full history of this format, see our knock-knock joke history page.