The crwth is a stringed musical instrument, a type of medieval bowed lyre associated particularly with Wales, although played more widely in Europe.

The instrument went out of fashion in Wales by about the 17th century (largely supplanted by the more versatile violin), and earlier elsewhere. There are three extant original Welsh instruments (currently in museums in Cardiff, Aberystwyth and Warrington), and numerous carvings, manuscript illustrations and written descriptions of the crwth.

The crwth consists of a fairly simple box construction with a flat, fretless fingerboard and six gut strings, usually tuned GgDdCc. The G strings run parallel to the fingerboard, but not over it, so these are used as drones, either plucked or bowed. The remaining strings are usually bowed with a short horsehair and wood bow. Due to the limited compass, the tuning and the flat bridge, the instrument is harmonically limited but is capable of producing a remarkably full, rich sound nonetheless. One characteristic feature of the crwth bridge is that one side of it goes through a soundhole and rests on the back of the instrument. Although it has been conjectured that this is a primitive attempt at a soundpost (which the instrument lacks), it is more likely that it is designed to take some of the weight of the strings off the belly of the instrument (since this is flat and unbraced, it is much weaker than the belly of a violin).

The tuning referred to above is mentioned in several manuscript sources of information about the crwth and is believed to have been the standard tuning for the instrument. It is, however, likely that different tunings would have been employed, as was and still is the case with many other stringed instruments.

A small number of modern reconstructions of the crwth have been made and there are a handful of musicians reviving the tradition of playing this instrument. The repertoire of surviving crwth tunes is very small, although many other traditional tunes can be adapted for the instrument and new tunes are being written for it.