The genius of Joni Mitchell's songs and performances has been entrancing listeners since the 1960s. But one of the most important qualities of her music has evaded most of her fans: open tunings.

Mitchell, who turns 69 on Wednesday, has employed more than 50 different tunings in the compositions she's recorded since her 1968 debut album Songs To a Seagull. In fact, she's rarely recorded in standard tuning, with the best-known exceptions being "Urge For Going," which was also a hit for folk hero Tom Rush, and "Tin Angel." Listen to the beginning of her 1974 pop hit "Free Man in Paris" and you'll hear the distinctive ring of her D-A-D-G-B-D tuning, sometimes called D modal tuning. Or 1970's "Big Yellow Taxi," which bounces along in open E tuning (E-B-E-G#-B-E).

Early in her career, Mitchell's penchant for open tunings was inspired by the country blues players she heard on records and encountered on gigs. Beginning with open D and open G, she began to map out her own territory and develop a sound that would set her apart from most of the other young voices on the blossoming '60s folk scene.

If you're familiar with Mitchell's music, consider using her songs as a springboard for exploring open tunings on your own. And if you're not, I'd recommend delving into her beautiful and inventive catalog, which runs from the classic folk realm to the heights of freewheeling jazz explorations under the inspiration and tutelage of Charles Mingus.

Like many folk artists, Mitchell is also a fan of the capo, or "cheater," as the blues elders referred to the device without a hint of distain. You can hear her combine open E with a capo on the fourth fret of "The Circle Game," one of her most famous early compositions on the 1968 album of the same name. If you try tackling the tune, take stock of the lilting, gently swinging way Mitchell strums - perhaps a precursor to the passion for jazz that would come to guide her music as the '70s reached their end.

Mitchell's choice of tunings has become more intensely personal as her music has progressed. On 1994's Grammy winning Turbulent Indigo, "The Magdalene Laundries" is built on her B-F#-B-E-A-E tuning, producing a striking and distinctive six-string sound. She reportedly came up with the tuning based on the pitch of a bird's call.

Three other tunings she's notably drawn upon are D-A-E-F#-A-D, for "Cherokee Sunset"; D-A-E-G-A-D for "Cool Water"; and D-F#-C#-E-F#-B for the majestic "Hejira."

Try some of these tunings yourself. Let the open chords ring in your ears and try placing your fingers on the two high strings in the second, third and fifth fret positions as you strum, to discover the sounds that emerge. And even better than using these tunings to play Mitchell's songs, just barre them as you like; travel up and down the guitar's neck and let your imagination fly. That's the kind of trial and error playing that led Mitchell down the road to discovering and mapping her own vocabulary in the first place, and it could also become part of your own musical evolution and revolution.