An octave twelve is a type of 12-string guitar

Guitar

The guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...

 fitted with a short-scale neck and a small solid body. It is tuned one octave

Octave

In music, an octave is the interval between one musical pitch and another with half or double its frequency. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems"...

 higher than a standard guitar, giving it the tonal range of a mandolin

Mandolin

A mandolin is a musical instrument in the lute family . It descends from the mandore, a soprano member of the lute family. The mandolin soundboard comes in many shapes—but generally round or teardrop-shaped, sometimes with scrolls or other projections. A mandolin may have f-holes, or a single...

, and enabling a guitarist to achieve a mandolin sound without learning mandolin fingering. The effect is similar to that of capo

Capo

A capo is a device used on the neck of a stringed instrument to shorten the playable length of the strings, hence raising the pitch. It is frequently used on guitars, mandolins, and banjos. G.B...

ing a standard 12-string guitar at its twelfth fret

Fret

A fret is a raised portion on the neck of a stringed instrument, that extends generally across the full width of the neck. On most modern western instruments, frets are metal strips inserted into the fingerboard...

. However, unlike a standard 12-string guitar, the courses

Course (music)

A course is a pair or more of adjacent strings tuned to unison or an octave and usually played together as if a single string. It may also refer to a single string normally played on its own on an instrument with other multi-string courses, for example the bass string on a nine string baroque...

 of strings tuned in unison, rather than in octave

Octave

In music, an octave is the interval between one musical pitch and another with half or double its frequency. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems"...

s.

The octave twelve was invented by engineers at Vox

Vox (musical equipment)

Vox is a musical equipment manufacturer which is most famous for making the Vox AC30 guitar amplifier, the Vox Continental electric organ, and a series of innovative but commercially unsuccessful electric guitars and bass guitars...

, which sold the octave twelve as the "Mando-guitar" from 1964 to 1968. Notable users of the Mando-guitar include Brian Jones

Brian Jones

Lewis Brian Hopkins Jones , known as Brian Jones, was an English musician and a founding member of the Rolling Stones....

 of The Rolling Stones

The Rolling Stones

The Rolling Stones are an English rock band, formed in London in April 1962 by Brian Jones , Ian Stewart , Mick Jagger , and Keith Richards . Bassist Bill Wyman and drummer Charlie Watts completed the early line-up...

, and George Harrison

George Harrison

George Harrison, MBE was an English musician, guitarist, singer-songwriter, actor and film producer who achieved international fame as lead guitarist of The Beatles. Often referred to as "the quiet Beatle", Harrison became over time an admirer of Indian mysticism, and introduced it to the other...

 of The Beatles

The Beatles

The Beatles were an English rock band, active throughout the 1960s and one of the most commercially successful and critically acclaimed acts in the history of popular music. Formed in Liverpool, by 1962 the group consisted of John Lennon , Paul McCartney , George Harrison and Ringo Starr...

, who used it prominently on the song "Words of Love." Most modern octave twelves are modeled after the distinctive body shape of the Vox Mando-guitar.