Walk the Line is a film chronicling the life of Johnny Cash, American country singer, focusing on his younger life, his romance with June Carter and his ascent to the country music scene, with material taken from his autobiographies. The title is taken from the title of one of Cash's best known songs, "I Walk the Line".

Walk the Line's production budget is estimated to have been $28,000,000.

The film previewed at the Telluride Film Festival on September 4, 2005 and went into wide release on November 18.

The film details Cash's (Phoenix) life from his growing up as the son of a cotton picker in rural Arkansas to his drug addiction and subsequent rescue by future wife June Carter (Witherspoon) in his famous concert at Folsom Prison.

In the opening scene, we see an outside shot of Folsom Prison, where the grounds are quiet, and the two solitary guards on their perch peer towards the main building. The camera moves towards the prison as faint music plays in the background. As the camera passes empty halls and cells, the music becomes louder and clearer, and cheering of inmates can be heard. The camera settles on an shot of inmates cheering as Cash's band is playing a loop of notes. A buzz saw sits ominously on a table in the center of the screen, as a solitary hand casually strokes the blades. After repeated calling, we are made aware that the hand belongs to Cash, and it is later revealed that the voice belongs to the prison's Warden, calling for him to go on stage.

The next scene depicts Cash as a boy (then called "J.R.") and his brother Jack listening to the radio, and hearing a 10-year-old June Carter singing, providing a foreshadow into J.R.'s obsession with her in the future. The next few establishing scenes provide a reference point from which the movie brings up later on, such as Foghorn Leghorn's line about keeping his feathers numbered in case of an emergency.

Early in the movie, Cash and Jack discuss their different strengths and weaknesses in regard to the Bible and hymns. Jack, who is training to become a pastor, and therefore "needs to know the Bible front to back", is much better at dealing with the wording and stories of the Bible. J.R., who can sing well like his mother, is very adapt to the hymns they sing at church. A few scenes later, Jack is sawing wood as a job for a neighbor when Johnny declares it to be boring, and would rather be somewhere else. With Jack's permission, he leaves to go fishing. As he is walking back home, he is intercepted by his father, flush with blood stains on his overalls, asking "Where have you been?"

J.R.'s relationship with his father was strained since he was young, yet was made much more severe with the death of Jack. Their relationship is a central plot device throughout the whole film, and is instrumental in Cash's fight against narcotics.

Told (twice) that wearing black made him look like he was going to a funeral, Cash replies, "Maybe I am."

The audience is made aware of Cash's problems with his first wife early on in the film, when she wants him to move to get a job with her father, and he wants to become a musician in Memphis.

In one of the last scenes of the film, the Folsom concert is revisited, with Carter and Cash united again.