Most guitarists will have a 12 String somewhere in their collection.
They might not use it much, but they will defend that and the rest of their guitars to the death if you question why they have so many or need so many different models.
So what does a 12 string do above it's 6 string counterparts?
Tuning
The main difference is afforded by the extra strings. Each string has a thinner, higher counterpart which is tuned an octave higher - apart from the upper B and E strings which are both tuned to the same octave. This gives the 12 string a much different, broader sound.
Examples of the sound can be heard in Led Zeppelin's 'Stairway to Heaven' (the soft guitar parts), Bachmann Turner Overdrive's 'You ain't seen nothin' yet' (main riff) and Rod Stewart's 'Maggie May' - an eclectic mix that goes much further. It's also a staple instrument of The Eagles, The Who, Crosby Stills and Nash, Bon Jovi and extended to modern artists like Rush, Opeth and System of a Down.
Maybe one of the most famous and well known 12 string parts - The Eagles, 'Hotel California'
The extra strings allow the guitar to create a natural 'chorus' effect without needed lots of effects pedals and amplifiers. It makes the perfect accompanying instrument to any acoustic music, filling in subtly some lower and higher frequencies, and allowing the other members of the band to expand their playing into solo passages or other chord inversions.
Thanks to recent advances in guitar building, 12 Strings are nowhere near as expensive as they used to be. For a budget model, the Rocket SW205/12 comes in at under £100 - great value for money for a beginner or the curious 6 string player looking to expand.
For the more discerning player or someone looking for a more professional feel, there's the Yamaha FG720S.
Whether you're looking to expand your sound, buy a gift for the guitarist who has everything or looking to just experiment - the 12 string can be the ideal instrument.