"I Walk the Line" is a song written and recorded in 1956 by Johnny Cash. After three attempts with moderate chart ratings, it became Cash's first number one hit on the Billboard charts. It reached number 17 on the US pop charts. It remained on the record charts for over 43 weeks, and sold over 2 million copies. It has also been used on many LP's released from Sun Records, such as With His Hot and Blue Guitar, Sings the Songs That Made Him Famous, and Sings Hank Williams. It was the title song for a 1970 film starring Gregory Peck.

The unique chord progression for the song was inspired by backwards playback of guitar runs on Cash's tape recorder while he was in the Air Force stationed in Germany. Later in a telephone interview, Cash stated, “I wrote the song backstage one night in 1956 in Gladewater, Texas. I was newly married at the time, and I suppose I was laying out my pledge of devotion." After the writing of the song Cash had a discussion with fellow performer Carl Perkins who encouraged him to adopt "I Walk the Line" as the song title. Cash originally intended the song as a slow ballad, but producer Sam Phillips preferred a faster arrangement, which Cash grew to like as the uptempo recording met with success.

Once while performing the song on his TV show, Cash told the audience, with a smile, "People ask me why I always hum whenever I sing this song. It's to get my pitch." The humming was necessary since the song required Cash to change keys several times while singing it.

The song's lyrics refer to marital fidelity, personal responsibility, and avoiding temptation and criminal behavior.

The song was originally recorded at Sun Studio on April 2, 1956, and was released on May 1. It spent six weeks at the top spot on the U.S. country Juke Box charts that summer, one week on the C&W Jockey charts and number two on the C&W Best Seller charts. "I Walk the Line" crossed over and reached number 19 on the pop music charts.

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