The Conversation is a 1974 American mystery / psychological thriller film written, produced, and directed by Francis Ford Coppola, which received many awards including (equivalent of) the Palme d'Or in 1974.
It stars Gene Hackman, who has named the film his favorite of all those he has made.
New Hollywood
Period marked by a great creative freedom left to directors, eventually with complex, uneasy and non consensual content. Coppola, one of the most prominent example of that current, and who wrote and directed the movie, considers this film his most personal project.
Ford Coppola
Long career starting in 1963 up to these days, with more than 20 movies as director.
Started making horror thriller, comedy, etc.
He's most known for The Godfather (1972). The Conversation was possible thanks to the success of The Godfather, and sits right between the part 1 and 2 of The Godfather. Later: Apocalypse Now.
Context
Watergate: FBI agents used the same surveillance and wire-tapping equipment - but the movie was filmed before the before the most revelatory Watergate stories broke in the press, and Coppola claimed that it was purely coincidental.
The character of Harry Caul was inspired by surveillance technology expert Martin Kaiser, who also served as a technical consultant on the film. Also inspired by Herman Hesse's novel "Steppenwolf".
Theme
"Francis had seen [it] a year or two before, and had the idea to fuse the concept of Blowup with the world of audio surveillance."
Technology: Blow up shows the power of images, The conversation builds up on the power of sounds, what Brian de Palma did also in "Blow Out" 8 years after.
Images and sound are naturally very dear to movie makers: they are the 2 pillars of cinema.
These movies also question the question of responsibilities and morality for the people who create and/or use advanced technologies for questionable purposes.
In a way it's also a variation on the "Rashomon effect": the unreliability of witness testimonies, even when those are collected by technological means.
Surveillance
A reference in a sub-genre that has a long history... and a very promising future.
More specifically, this movie explores psychological aspects of the agents who engage in activities, eg. Surveillance <-> paranoia.
Ref: Blow up, Blow out, The life of others, Citizen 4, etc. And many sci-fi movies: Metropolis, M, 1984, Minority Report, Brazil, 2001 Space Odyssey...
First shot
The movie is often referred to from its first scene, as if the operator were a sniper and the shotgun microphone were a weapon / riffle. It's like an allegory mixing image (camera), sound (microphone), and the weaponisation of technology. Coppola mentioned that he used the camera as an eavesdropping device.
With a reference to a famous sci-fi book, we definitely live in a Brave New World.