After working with the producer Bruno Pésery on his previous four films, Alain Resnais took up an invitation from Jean-Louis Livi to make a new one. For a subject, he was drawn to the novels of Christian Gailly by the author's "ironic and melancholy voice", and also by the musical quality of his writing and dialogue. He settled upon L'Incident, and obtained Gailly's permission to adapt it for the cinema when he undertook not to require Gailly's involvement in the preparation of the script. Although Resnais had worked closely with novelists on some earlier projects, this was the first time in his career that he took an existing novel as the basis for a film.
Marguerite Muir is a dentist, single and middle-aged, independent and unpredictable of mood. Georges Palet is in his late 50s, married, and unemployed; he too is temperamental, and burdened by something in his past (unexplained but possibly criminal). When Georges discovers the discarded wallet from Marguerite's stolen handbag and hands it in to the police station, he allows himself to imagine the door opening to a romantic encounter. Marguerite initially has other ideas, but is later drawn towards Georges. Georges's wife Suzanne, Marguerite's best friend Josépha and two policemen are drawn into the entanglement of their lives. Georges and Marguerite share a passion for aviation, which leads to a flight with Suzanne in Marguerite's plane, while a farmer watches apprehensively from below. There is an uncertain resolution of their adventure, and the film ends with an enigmatic question from the farmer's daughter.
- Sabine Azéma as Marguerite Muir
- André Dussollier as Georges Palet
- Anne Consigny as Suzanne, the wife of Georges
- Emmanuelle Devos as Josépha, Marguerite's partner in their dental practice
- Mathieu Amalric as Bernard de Bordeaux, a local police officer
- Michel Vuillermoz as Lucien d'Orange, another police officer
- Sara Forestier as Élodie, the daughter of Georges and Suzanne
- Nicolas Duvauchelle as Jean-Mi, Élodie's husband
- Vladimir Consigny as Marcellin, the son of Georges and Suzanne
- Annie Cordy as the neighbour of Marguerite
- Roger Pierre as Marcel Schwer, Marguerite's elderly patient
- Isabelle Des Courtils as Madame Larmeur (the mother with a laptop)
- Candice Charles as Elodie Larmeur (the little girl in bed)
- Patrick Mimoun as Jean-Baptiste Larmeur (the farmer in a field)
- Édouard Baer (voice) as the narrator
In preparing the script, Resnais used the dialogue from Gailly's novel, since this had been the element which had particularly attracted him initially, and he repeatedly made reference back to Gailly's style of writing when seeking a rhythm for the film narrative or a visual equivalence for the hesitations and contradictions within his sentences. He also encouraged his set designer Jacques Saulnier and his director of photography Éric Gautier to follow the spirit of Gailly in the way that they used bold and contrasted elements of colour in the film's visual design. The composer of the music Mark Snow provided similarly varied and clear-cut musical styles for different episodes.
In the two principal roles, Resnais used actors with whom he had worked many times before: Sabine Azéma, making her ninth appearance in a Resnais film, and André Dussollier, making his seventh appearance. For the main supporting roles Resnais chose three actors (Anne Consigny, Emmanuelle Devos and Mathieu Amalric) who were new to his films, but who had all worked together in films directed by Arnaud Desplechin (alongside cameraman Éric Gautier). (Resnais acknowledged his admiration for Desplechin elsewhere.) Roger Pierre, who first worked for Resnais on Mon oncle d'Amérique (1980), played the small part of the dentist's elderly patient who says that this will be the last dental appointment he needs; Pierre died in January 2010.
The story is presented with the help of a voiceover narrator (Édouard Baer) who is almost another character in the film since he seems to be inventing what we see on the spot, complete with hesitations and omissions and changes of tone. It is left to the audience to decide whether his observations about the characters that the audience watches are to be believed or not.
Resnais explained his alteration of the title to Les Herbes folles as a recognition that L'Incident would not work as successfully as a title in a cinematic context as it did for the novel. His "wild grass" refers to a plant that grows in a place where it has no hope of developing: in a crack in a wall, or a ceiling. In the film his principal characters are "two people who have no reason to meet, no reason to love each other". The image reflects the stubbornness of Georges and Marguerite "who are incapable of resisting the desire to carry out irrational acts, who display incredible vitality in what we can look on as a headlong rush into confusion".
The film incorporates a number of references to cinema, notably in excerpts from and discussion of the American war film The Bridges at Toko-Ri (1954). The fanfare which traditionally accompanied the 20th Century Fox logo is featured at two points, marking off a section of the film within the film. For one major sequence, Jacques Saulnier constructed in the studio an extensive set of a street scene in which a local cinema, evocative of bygone years, provides the focal point.
Towards the end of the film, there is an interpolated quotation (from Flaubert's L'Éducation sentimentale): "N'importe, nous nous serons bien aimés." ["No matter, we shall have loved each other well."]
The film was a French-Italian production budgeted at €11.1 million. Filming took place at the Arpajon studios near Paris.
The film was first shown at the 2009 Cannes Film Festival in competition, and it resulted in a special jury prize for Alain Resnais as a "lifetime achievement award for his work and exceptional contribution to the history of cinema".
When the film was released in France in November 2009, reviews were predominantly favourable, with frequent reference to the originality and youthfulness of this work from an 87 year old director. Public reaction was more varied, but the film achieved over 380,000 ticket sales in its first four weeks of distribution.
At the French César Awards 2010, Les Herbes folles was nominated for four awards including Best Film and Best Cinematography.
Reactions to the film among English-language reviewers indicated a more polarised assessment, with a contrast between those who were unconvinced about either the coherence or the significance of the story and those who savoured its sense of humour and cinematic invention. Roger Ebert considers the movie a "young man’s film made with a lifetime of experience" and calls it a "visual pleasure."