The traditional Welsh costume is a costume worn by rural women in Wales. The costume was identified as being different from that worn by the rural women of England by many of the English visitors who toured Wales during the late 18th and early 19th centuries. It is very likely that what they wore was a survival of a pan-European costume worn by working rural women.

It is likely that the Welsh costume began as a rural costume (with regional variations in Wales) and became recognized as a traditional costume by the wives and daughters of the better off farmers who wore it for special occasions and when going to market to sell their produce.

From the 1880s, when the traditional costume had gone out of general use, selected elements of it became adopted as a National Costume. From then on it was worn by women at events such as Royal visits, by choirs, at church and chapel, for photographs and occasionally at eisteddfodau. It was first worn by girls as a celebration on Saint David's Day just before the First World War. The costume is now recognised as the national dress of Wales.