There are three main types of bouzouki:

• Greek Tetrachordo - four pairs of strings tuned to C3C4 - F3F4 - A3A3 - D4D4. This tuning pattern is the same as the first (highest) four strings of a guitar although shifted down a tone, so that standard guitar chords can be used on it.
• Greek Trichordo - three pairs of strings tuned to D3D4 - A3A3 - D4D4. This is the traditional bouzouki.
• Irish Bouzouki - four pairs of strings, usually tuned to G2G2 - D3D3 - A3A3 - D4D4.

Andy Irvine, who must be considered one of the fathers of the Irish Bouzouki, has a number of instruments at different pitches, most of them made by Stefan Sobell. He always keeps them tuned to a variation of the GDAD tuning:

• Mandola - a larger, deeper mandolin, tuned DAEA, which is the same pattern as GDAD but a fifth higher.
• 'Bassouki' - a larger, deeper bazouki tuned to CGDG, a fifth lower than the standard bazouki.
• Octave mandola - tuned to GDAD like a bouzouki but with octave strings to give it a different sound

Alternative Tunings for Irish Bouzouki

There are a number of alternative tunings used for the Irish Bouzouki:

• GDAE - like a mandolin but an octave lower. Because all the strings are a fifth apart, the fingering is more logical, although the long scale makes playing tunes quite tricky. The bouzouki has a scale length about the same as a cello, so cello fingering patterns could be used. Many players just stick on a capo to shorten the strings, making it easier to play tunes, but limiting the instrument - why buy a long scale instrument and then convert it into a short scale one?
• GDGC - this has been suggested although I haven't seen anybody who uses it. It should allow tunes to be played much more easily on the top three strings while using the bass string as a G drone.