The scenario is of a person knocking on the front door to a house. The teller of the joke says, "Knock, knock!"; the recipient responds, "Who's there?" The teller gives a name (such as "Noah") or a description (such as "Police") or something that purports to be a name (such as "Needle"). The other person then responds by asking the caller's surname ("Noah who?" "Police who?" "Needle who?"), to which the joke-teller delivers a pun involving the name ("Noah place I can spend the night?" "Police let me in—it's cold out here!" "Needle little help with the groceries!").
The formula of the joke is usually followed strictly, though there are cases where it is subverted:
As shown below, knock-knock jokes can take the form of simple puns on the name given, jokes specifically involving the door-knocking scenario, or puns on the "who?" phrase of the speaker.
A possible source of the joke is William Shakespeare's Macbeth; first performed in 1606. In Act 2, Scene 3 the porter is very hungover from the previous night. During his monologue he uses "Knock, knock! Who's there" as a refrain while he is speaking:
Writing in the Oakland Tribune, Merely McEvoy recalled a style of joke from around 1900 where a person would ask a question such as "Do you know Arthur?", the unsuspecting listener responding with "Arthur who?" and the joke teller answering "Arthurmometer!"
A variation of the format in the form of a children's game was described in 1929. In the game of Buff, a child with a stick thumps it on the ground, and the dialogue ensues:
In 1936, Bob Dunn authored the book Knock Knock: Featuring Enoch Knox.
In 1936, the standard knock-knock joke format was used in a newspaper advertisement. That joke was:
A 1936 Associated Press newspaper article said that "What's This?" had given way to "Knock Knock!" as a favorite parlor game. The article also said that "knock knock" seemed to be an outgrowth of making up sentences with difficult words, an old parlor favorite. A popular joke of 1936 was "Knock knock. Who's there? Edward Rex. Edward Rex who? Edward Rex the Coronation." Fred Allen's 30 December 1936 radio broadcast included a humorous wrapup of the year's least important events, including a supposed interview with the man who "invented a negative craze" on 1 April: "Ramrod Dank... the first man to coin a Knock Knock."
"Knock knock" was the catchphrase of music hall performer Wee Georgie Wood, who was recorded in 1936 saying it in a radio play, but he simply used the words as a reference to his surname and did not use it as part of the well-known joke formula. The format was well known in the UK and US in the 1950s and 1960s before falling out of favor. It then enjoyed a renaissance after the jokes became a regular part of the badinage on Rowan & Martin's Laugh-In.
According to the World Encyclopedia of Cartoons, published by Chelsea House, New York and London 1980, cartoonist Bob Dunn "invented the Knock Knock joke in a million selling book" distributed by Whitman Publishing in 1936. One of the answers on the game show Jeopardy! broadcast on December 27, 1989, was "Dunn, Dunn Who…Creator of this Joke in 1936". The question in response: "What is the Knock Knock joke?"
- Linton Weeks (3 March 2015). "The Secret History of Knock-Knock Jokes". Retrieved 27 June 2016.
- Henry Bett (1929). The games of children: their origin and history. Singing Tree Press. p. 87.
- "Hee Haw News" p. 4. Rolfe Arrow. (Rolfe, Iowa). 10 September 1936.
- "'Knock Knock' Latest Nutsy Game For Parlor Amusement." P. 1.3 August 1936. Titusville Herald (Pennsylvania). Byline 2 August. New York.
- "Wallis Simpson 'not good looking'". The Daily Telegraph. 1 November 2010. Retrieved 7 November 2015.
- Allen, Fred; Hample, Stuart (2001). All the Sincerity in Hollywood--: Selections from the Writings of Radio's Legendary Comedian Fred Allen. Fulcrum Pub. p. 3. ISBN 978-1-55591-154-6.
- Rees, Nigel (2006). A Word in Your Shell-like: 6,000 Curious & Everyday Phrases Explained. Collins. p. 395. ISBN 978-0-00-722087-8.