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"), 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.
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:
Knock, knock! Who's there, i' the name of
Beelzebub? Here's a farmer, that hanged
himself on the expectation of plenty: come in
time; have napkins enow about you; here
you'll sweat for't.
Knock, knock! Who's there, in the other devil's
name? Faith, here's an equivocator, that could
swear in both the scales against either scale;
who committed treason enough for God's sake,
yet could not equivocate to heaven: O, come
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:
What says Buff?
Buff says Buff to all his men, And I say Buff to you again.
In 1936, the standard knock-knock joke format was used in a newspaper advertisement. That joke was:
Rufus the most important part of your house.
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.
- 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.
- Horn, Maurice. The World Encyclopedia of Cartoons. Chelsea House. ISBN 978-0-7910-4855-9.
- "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.