The Nashville Number System is a method of transcribing music by denoting the scale degree on which a chord is built. It was developed by Neal Matthews Jr. in the late 1950s as a simplified system for the Jordanaires to use in the studio and further developed by Charlie McCoy. It resembles the Roman numeral and figured bass systems traditionally used to transcribe a chord progression since the 1700s. The Nashville Number System was compiled and published in a book by Chas. Williams in 1988.
The Nashville Number System can be used by anyone, including someone with only a rudimentary background in music theory. Improvisation structures can be explained using numbers, and chord changes can be communicated mid-song by holding up the corresponding number of fingers. The system is flexible and can be embellished to include more information (such as chord color or to denote a bass note in an inverted chord). The system makes it easy for bandleaders, the record producer, or the lead vocalist to change the key of songs when recording in the studio or playing live since the new key has to be stated before the song is started. The rhythm section members can then use their knowledge of harmony to perform the song in a new key.