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Guitar style

While some of Mitchell's most popular songs were written on the piano, almost every song she composed on the guitar uses an open, or non-standard, tuning; she has written songs in some 50 tunings, playing what she has called "Joni's weird chords". The use of alternative tunings allows guitarists to produce accompaniment with more varied and wide-ranging textures. Her right-hand picking/strumming technique has evolved over the years from an initially intricate picking style, typified by the guitar songs on her first album, to a looser and more rhythmic style, sometimes incorporating percussive "slaps".

In 1995, Mitchell's friend Fred Walecki, proprietor of Westwood Music in Los Angeles, developed a solution to alleviate her continuing frustration with using multiple alternative tunings in live settings. Walecki designed a Stratocaster-style guitar to function with the Roland VG-8 virtual guitar, a system capable of configuring her numerous tunings electronically. While the guitar itself remained in standard tuning, the VG-8 encoded the pickup signals into digital signals which were then translated into the altered tunings. This allowed Mitchell to use one guitar on stage, while an off-stage tech entered the preprogrammed tuning for each song in her set.

Mitchell was highly innovative harmonically in her early work (1966–1972), incorporating modality, chromaticism, and pedal points. On her 1968 debut album Song to a Seagull, Mitchell used both quartal and quintal harmony in "The Dawntreader" and quintal harmony in "Song to a Seagull".

In 2003, Rolling Stone named her the 72nd-greatest guitarist of all time; she was the highest-ranked woman on the list.