A triangular frame harp traditional to Ireland and Scotland. It is known as cláirseach in Irish and clarsach in Scottish Gaelic.

The first instrument associated with the harping tradition in the Gaelic world was known as a cruit. This word may originally have described a different stringed instrument, being etymologically related to the Welsh crwth. It has been suggested that the word clarsach was coined in Scotland for the triangular frame harp which replaced the cruit.

The earliest descriptions of a European triangular frame harp (with a fore pillar) are found on carved 8th century Pictish stones. Pictish harps were strung from horsehair. The instruments apparently spread south to the Anglo Saxons who commonly used gut strings and then west to the Gaels of the Highlands and to Ireland.

In construction, the Irish and Scottish harp may in general be considered the same. A characteristic feature is the metal strings. The wires were attached to a massive soundbox typically carved from a single log, commonly of willow, although other woods including alder and poplar have been identified in extant harps. This harp also had a reinforced curved pillar and a substantial neck, flanked with thick brass cheek bands. The strings, usually played with the fingernails, produced a brilliant ringing sound. This type of harp is also unique amongst single row triangular harps in that the first two strings tuned in the middle of the gamut were set to the same pitch.

Because of the long-lasting resonance, the performer had to dampen strings which had just been played while new strings were being plucked, and this while playing rapidly. Contrary to conventional modern practice, the left hand played the treble and the right the bass.