Humour and jokes about one's mother-in-law (the mother of one's spouse) are a mainstay of comedy. The humour is based on the premise that the average mother-in-law often considers her son-in-law to be unsuitable for her daughter (or daughter-in-law unsuitable for her son), and usually includes the stereotype that mothers-in-law are generally overbearing, obnoxious, or unattractive. This has commonly been referred to as the "battle."
There is evidence that this joke dates back to Roman times: Satire VI by Juvenal says that one cannot be happy while one's mother-in-law is still alive. Most of the mother-in-law jokes are easily translatable to other languages and are easily understandable in most European cultures.
In a book on cartooning written by Dave Breger, the author lists a series of "tired gags," and gives a suggestion on how to exploit them. In his illustration, Breger and his wife go to a museum and see a Tyrannosaurus skeleton. Mrs. Breger says, "And no funny remarks, please, about that Mother called or something..."
A study of mothers-in-law by Dr. Pamela Cotterill found that "they tended not to be upset by jokes because they seemed so far fetched they couldn't apply to them, but they didn't find them funny". Cotterill also found that daughters-in-law didn't find them funny either, largely because they saw that one day they could be applied to them.
The jokes are considered offensive by some. A widely reported case is the that of the London borough where a workshop leaflet called "Cultural Awareness: General Problems" advised against using them. The leaflet states that "mother-in-law jokes, as well as offensively sexist in their own right, can also be seen as offensive on the grounds that they disrespect elders or parents." 
The stereotype is often portrayed on film and in popular entertainment.
- Viola Fields (Jane Fonda) in the film Monster-in-Law
- Adele Delfino (Celia Weston) on the television series Desperate Housewives
- Daisy Werthan in the play Driving Miss Daisy
- Endora (Agnes Moorhead) in the sitcom Bewitched , where she plays a witch who is not happy with the decision of her daughter to marry a normal human, and often uses her magic to cause trouble for him.
- Norma Speakman (Liz Smith) in the sitcom The Royle Family, who enjoys baiting son-in-law Jim.
- Luisa Dillner: Mothers-in-law are lovely, in their place. Their own place, that is - Commentators - Voices - The Independent
- Mothers and Daughters-in-Law: A Study of Intergenerational Relationships Between Family Women. Staffordshire Polytechnic, 1989
- Council denies ban on mother-in-law jokes (From Times Series)
- Council outlaws mother-in-law jokes - Telegraph