A knock-knock joke is a special kind of conversation that always begins with someone saying, "Knock-knock!" and then someone else asking, "Who's there?"
The basic format is as follows:
Joke-Teller: "Knock-knock!"
Joke-Hearer: "Who's there?"
Teller: "[name or word]"
Hearer: "[name or word] who?"
Teller: "[answer]"
Knock-knock jokes come from "do you know?" jokes in the 1900s and became very popular in the 1930s.[1]
An example of a knock-knock joke is:
Jenny: "Knock-knock!"
Penny: "Who's there?"
Jenny: "Cowsgo!"
Penny: "Cowsgo who?"
Jenny: "Cowsgo moo, not who!"
"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.
Knock-knock jokes have been used by Mr. Moose from Captain Kangaroo.