Acting debut of Sophie Marceau, who was discovered late in the process by casting director Françoise Menidrey after the then 13 year old with no drama training whatsoever had just days earlier joined a child modeling agency to earn some pocket money and auditioned by chance. The role immediately propelled her to international superstardom and she has since been consistently named as one of, if not the favorite celebrity of the French.
It was during filming that director Claude Pinoteau handed his young lead actress, 13 year old Sophie Maupu, a map of Paris, suggesting that she use it to choose a stage name, so the girl chose the Marceau avenue, to have the same initials as her real name, and thus became Sophie Marceau.
The film was not expected to have much success at release, debuting at the sixth place of the French box-office, but admissions kept growing day after day, eventually reaching and staying at the first place for a month and remaining in French theaters for 35 weeks, or over 8 months, becoming the most successful film of 1980 in France with 4,378,430 tickets sold, over Star Wars: Episode V - The Empire Strikes Back (1980). This was just that start of a major international success, with over 15 million tickets sold across Europe. By the time the film reached Italian screens in late 1981, the soundtrack's single "Reality", had been a huge hit for months and the film became a phenomenon, becoming the biggest film of the year in Italy, beating out E.T. the Extra-Terrestrial (1982) with nearly 8 million admissions, almost double that of France.
Georges Delerue, director Claude Pinoteau's usual composer of choice up to that point, advised him to instead turn to Michel Polnareff for a hip, modern feel, and the pop star signed on to the project. However, a few weeks prior to filming, Pinoteau was unconvinced by the tracks Polnareff, who was living in the United States at the time, sent over and was unable to reach him. It was then that Pinoteau, appreciative of Vladimir Cosma's work with director Yves Robert, particularly on Salut l'artiste (1973), asked production supervisor Marc Goldstaub to call the composer. Cosma, who was very busy with other projects that year and was taking a few days' holiday, turned the offer down, but then felt compelled to accept when he was called back by Gaumont head, executive producer Alain Poiré, despite being confused as to why he was being called upon despite never having composed a song and not being well-versed in the pop and rock feel the film demanded. He nevertheless set to work for nine months, studying the biggest successes of the past two decades to write the variety of ballads, rock and reggae tunes required. In the end, the featured single "Reality" became a number one hit in fifteen countries and over 27 million copies of the soundtrack were sold. It was one of Cosma's biggest successes and the first of a string of seven collaborations with Claude Pinoteau.
Claude Brasseur and Sophie Marceau play father and daughter here and in the sequel, The Party 2 (1982), but would reunite six years later to play lovers in Descent Into Hell (1986).