This type of harp has two identically-tuned parallel rows of nylon strings, two full sets of sharping levers, and its characteristic sound is that of a "waterfall of notes", or a rapid succession of repeated notes very much like a Welsh triple-strung harp. Because the harp has twice as many strings as its same-sized single-row counterparts, there is a capacity for intricate arrangements and complex harmonies, and the hands never run into one another, even on the smallest harp!

The difference in sound between a large single-course harp and a smaller double-strung harp is that the left (or lower) hand, which plays accompaniments, can actually play in a higher register, often above what the right hand is playing, because of the separate but identically tuned row of strings, and this produces a unique and beautiful echo effect.

Styles which are possible on a double-strung harp include:

• Welsh doubled-melody
• the polyrhythmic sound of the African Kora
• Medieval and Renaissance harpa doppia and Gothic Harp repertoire,
• which includes early music and some Baroque music
• All lever harp styles, including Celtic, Pop, Jazz, New Age
• South American music and rhythms
• Some classical styles

There is an historical double-strung harp called "harpa doppia", which was used in Spain and Italy. Unlike today's double harp, it had three partial rows of strings, with the diatonic row split between the left hand (bass notes) and the right (treble), and a chromatic row opposite those strings. The harpa doppia was developed in response to a growing need, in the 1500s, for accidentals, as music became more chromatic. Later, triple-strung harps may have seemed to be the answer to the limitations of the harp doppia, but they have no levers, and though accidentals are easily accessed, key changes are difficult at best.

The contemporary double-strung design, which is much more versatile, resulted from the desire for a harp which could be played like a triple-strung or a single-course lever harp, at will. Thus, two identically tuned rows of strings, with two full sets of levers for key changes, answered the need. It was designed in 1990 by harpist Liz Cifani and me, and Triplett Harps and Stoney End Harps built the first two contemporary designs. Later, other companies caught on, and at this writing in 2000, many harp makers are offering double-strung harps.

There is a video available with instruction for double-strung harp, "An Introduction to Multi-Course Harps", which also features cross-strung instruction. It was produced by Argent Fox Harps.