Expatriate American actor Eddie Constantine plays Lemmy Caution, a trenchcoat-wearing secret agent. Constantine had already played this or similar roles in dozens of previous films; the character was originally created by British pulp novelist Peter Cheyney. However, in Alphaville, director Jean-Luc Godard moves Caution away from his usual twentieth century setting, and places him in a futuristic sci-fi dystopia, the technocratic dictatorship of Alphaville.
Lemmy Caution is a secret agent with the code number of 003 from "the Outlands". Entering Alphaville in his Ford Mustang, called a Ford Galaxie, he poses as a journalist named Ivan Johnson, and claims to work for the Figaro-Pravda. He wears a tan overcoat that stores various items such as an M1911A1 Colt Commander semi-automatic pistol. He carries a cheap Instamatic camera (new in 1965) with him and photographs everything he sees, particularly the things that would ordinarily be unimportant to a journalist.
Caution is, in fact, on a series of missions. First, he searches for the missing agent Henri Dickson (Akim Tamiroff); second, he is to capture or kill the creator of Alphaville, Professor von Braun (Howard Vernon); lastly, he aims to destroy Alphaville and its dictatorial computer, Alpha 60. Alpha 60 is a sentient computer system created by von Braun which is in complete control of all of Alphaville.
Alpha 60 has outlawed free thought and individualist concepts like love, poetry, and emotion in the city, replacing them with contradictory concepts or eliminating them altogether. One of Alpha 60's dictates is that "people should not ask 'why', but only say 'because'". People who show signs of emotion (weeping at the death of a wife, or smiling) are presumed to be acting illogically, and are gathered up, interrogated, and executed. In an image reminiscent of George Orwell's concept of Newspeak, there is a dictionary in every hotel room that is continuously updated when words that are deemed to evoke emotion become banned. As a result, Alphaville is an inhuman, alienated society.
Caution is told that men are killed at a ratio of fifty to every one woman executed. He also learns that Swedes, Germans and Americans assimilate well with Alphaville. Images of the E = mc² and E = hf equations are displayed several times throughout the film as symbols of the regime of logical science that rules Alphaville. At one point, Caution passes through a place called the Grand Omega Minus, from where brainwashed people are sent out to the other "galaxies" to start strikes, revolutions, family rows and student revolts.
As an archetypal American anti-hero private eye in trench-coat and with weathered visage, Lemmy Caution's old-fashioned machismo conflicts with the puritanical computer (Godard originally wanted to title the film Tarzan versus IBM). The opposition of his role to logic (and that of other dissidents to the regime) is represented by faux-quotations from Capitale de la douleur (Capital of Pain), a book of poems by Paul Éluard.
Caution meets Dickson, who soon dies in the process of making love to a "Seductress Third Class". Caution then enlists the assistance of Natacha von Braun (Anna Karina), a programmer of Alpha 60 who is also the daughter of Professor von Braun (although she says "I have never met him"). Natacha is a citizen of Alphaville, and when questioned says she does not know the meaning of "love" or "conscience". Caution falls in love with her, and his love introduces emotion and unpredictability into the city that the computer has crafted in its own image. Natacha discovers, with the help of Lemmy Caution, that she was actually born outside of Alphaville. (The city name is given as Nueva York—Spanish for New York—instead of either the original English name or the French literal rendering "Nouvelle York".)
Professor von Braun (the name is a reference to the German rocket scientist Wernher von Braun) was originally known as Leonard Nosferatu (a tribute to F. W. Murnau's film Nosferatu), but Caution is repeatedly told that Nosferatu no longer exists. The Professor himself talks infrequently, referring only vaguely to his hatred for journalists, and offering Caution the chance to join Alphaville, even going so far as to offer him the opportunity to rule a galaxy. When he refuses Caution's offer to go back to "the outlands", Caution kills him with a pistol shot.
Alpha 60 converses with Lemmy Caution several times throughout the film, and its voice is seemingly ever-present in the city, serving as a sort of narrator. Caution eventually destroys or incapacitates it by telling it a riddle that involves something Alpha 60 can not comprehend: poetry (although many of Alpha 60's lines are actually quotations from the Argentine poet Jorge Luis Borges; the opening line of the film, along with others, is an extract of Borges's essay "Forms of a Legend" and other references throughout the movie are made by Alpha 60 to Borges's "A New Refutation of Time"). The concept of the individual self has been lost to the collectivized citizens of Alphaville, and this is the key to Caution's riddle.
At the end, as Paul Misraki's musical score reaches its climax, Natacha realizes that it is her understanding of herself as an individual with desires that saves her, and destroys Alpha 60. The film ends with her line, "Je vous aime" ("I love you").
Despite its futuristic scenario, Alphaville was filmed entirely in and around Paris and no special sets or props were constructed. Buildings used were the Electricity Board building for the Alpha 60 computer centre and the Hotel Sofitel Paris le Scribe.
Constantine came to the film through producer André Michelin, who had the actor under contract. Constantine had become a popular actor in France and Germany through his portrayal of tough-guy detective Lemmy Caution in a series of earlier films. Godard appropriated the character for Alphaville but according to director Anne Andreu, Godard's subversion of the Lemmy Caution "stereotype" effectively shattered Constantine's connection with the character—he was never again offered a Lemmy Caution role and reportedly said that he was shunned by producers after Alphaville was released.
The opening section of the film includes an unedited sequence that depicts Caution walking into his hotel, checking in, riding an elevator and being taken through various corridors to his room. According to cinematographer Raoul Coutard, he and Godard shot this section as a continuous four-minute take. Part of this sequence shows Caution riding an elevator up to his room, which was achieved thanks to the fact that the hotel used as the location had two glass-walled elevators side by side, allowing the camera operator to ride in one lift while filming Constantine riding the other car through the glass between the two. However, as Coutard recalled, this required multiple takes, since the elevators were old and in practice they proved very difficult to synchronize.
Like most of Godard's films, the performances and dialogue in Alphaville were substantially improvised. Assistant director Charles Bitsch recalled that, even when production commenced he had no idea what Godard was planning to do. Godard's first act was to ask Bitsch to write a screenplay, saying that producer Michelin had been pestering him for a script because he needed it to help him raise finance from backers in Germany (where Constantine was popular). Bitsch protested that he had never read a Lemmy Caution book, but Godard simply said "Read one and then write it." Bitsch read a Caution book, then wrote a 30-page treatment and brought it to Godard, who said "OK, fine" and took it without even looking at it. It was then given to Michelin, who was pleased with the result, and the "script" was duly translated into German and sent off to the backers. In fact, none of it even reached the screen and according to Bitsch the German backers later asked Michelin to repay the money when they saw the completed film.
Jean Cocteau exerted significant influence on Godard's films, and parallels between Alphaville and Cocteau's 1950 film Orpheus are evident. For example, Orphée's search for Cégeste and Caution's for Henri Dickson, between the poems Orphée hears on the radio and the aphoristic questions given by Alpha 60, between Orphée's victory over Death through the recovery of his poetic powers and Caution's use of poetry to destroy Alpha 60. Moreover, Godard openly acknowledges his debt to Cocteau on several occasions. When Alpha 60 is destroyed, for instance, people stagger down labyrinthine corridors or cling blindly to the walls like the inhabitants of Cocteau's "Zone de la mort", and, at the end of the film, Caution tells Natacha not to look back. Godard compares this scene with Orphée's warning to Eurydice, and it is also possible to detect a reference here to the biblical flight from Sodom.
The voice of Alpha 60 was performed by a man with a mechanical voice box replacing his cancer-damaged larynx. It is inspired by the hypnotic power of Mabuse's disembodied voice in the 1933 film The Testament of Dr Mabuse.
The film production company Alphaville Pictures, co-founded in 2003 by Danish director Christoffer Boe, is named after the film.
Alphaville also inspired the London-based organisation Alpha-ville, to create a festival that explores the intersection between art, society, and technology.
Alphaville is mentioned in Lovebug Starski's song, "Amityville (The House on the Hill)" (1986).
Jazz bassist and composer William Parker recorded Alphaville Suite, inspired by the film, in 2007.
German synthpop band Alphaville took their name from the film.
Bryan Ferry's 13th studio album, Olympia, includes a track titled "Alphaville", which takes its name from this film. The track was written by Bryan Ferry and David A. Stewart.
Haruki Murakami's novel After Dark features a love hotel named after the film.
There is also a high-end suburb outside of São Paulo that is named after the film.
The music video for the song Linger by the Irish rock band The Cranberries was influenced by this film.