A steel-strung guitar with 12 strings in 6 courses, which produces a thicker, more ringing tone than a standard 6-string guitar. Typically, the strings of the lower 4 courses are tuned in octaves, with those of the upper 2 courses tuned in unison. The gap between the strings within each dual-string course is narrow, and the strings of each course are fretted and plucked as a single unit. The neck is wider, to accommodate the extra strings, and is similar to the width of a classical guitar neck. The sound, particularly on acoustic instruments, is fuller and more harmonically resonant than 6-string instruments.

Twelve-string guitars are made in both acoustic and electric forms.