American romantic comedy film directed, produced and co-written by Billy Wilder. It stars Marilyn Monroe, Tony Curtis and Jack Lemmon, with George Raft, Pat O'Brien, Joe E. Brown, Joan Shawlee, Grace Lee Whitney and Nehemiah Persoff in supporting roles. The screenplay by Wilder and I. A. L. Diamond is based on a screenplay by Robert Thoeren and Michael Logan from the 1935 French film Fanfare of Love. The film is about two musicians who disguise themselves by dressing as women in order to escape from mafia gangsters whom they witnessed committing a crime.

Billy Wilder wrote the script for the film with writer I.A.L. Diamond. The plot was based on a screenplay by Robert Thoeren and Michael Logan for the 1935 French film Fanfare of Love. The original script for Fanfare of Love was untraceable, so Walter Mirisch found a copy of the 1951 German remake, Fanfares of Love. He bought the rights to that script, and Wilder worked with this to produce a new story. Both films follow the story of two musicians in search of work, but Wilder created the gangster subplot that keeps the musicians on the run.

The studio hired female impersonator Barbette to coach Lemmon and Curtis on gender illusion for the film.

Monroe worked for 10 percent of the gross in excess of $4 million, Curtis for 5 percent of the gross over $2 million, and Wilder for 17.5 percent of the first million after break-even and 20 percent thereafter.

There were many problems with Marilyn Monroe, who lacked concentration and suffered from an addiction to pills. She was constantly late to set, and could not memorize many of her lines, averaging 35–40 takes for a single line according to Tony Curtis. The line "It's me, Sugar" took 47 takes to get correct because Monroe kept getting the word order wrong, saying either "Sugar, it's me" or "It's Sugar, me". Tony Curtis and Jack Lemmon made bets during the filming on how many takes she would need to get it right.

Three days were scheduled for shooting the scene with Shell Jr. and Sugar at the beach, as Monroe had many complicated lines, but the scene was finished in only 20 minutes.

Billy Wilder spoke in 1959 about making another film with Monroe: "I have discussed this with my doctor and my psychiatrist and they tell me I'm too old and too rich to go through this again." But Wilder also admitted: "My Aunt Minnie would always be punctual and never hold up production, but who would pay to see my Aunt Minnie?" He also stated that Monroe played her part wonderfully.

The film's iconic closing line, "Nobody's perfect," was never supposed to be in the final cut. Diamond and Wilder put it in the script as a "placeholder" until they could come up with something better, but they never did.