Patagonian Welsh is a variety of the Welsh language spoken in Y Wladfa, the Welsh settlement in Patagonia, Chubut Province, Argentina. The decimal numeral system used in Modern Welsh originated in Patagonia in the 1870s, and was subsequently adopted in Wales in the 1940s as a simpler counterpart to the traditional vigesimal system, which still survives in Wales.

Y Wladfa, also occasionally Y Wladychfa Gymreig, refers to the establishment of settlements by Welsh colonists and immigrants in the Argentine Patagonia, beginning in 1865, mainly along the coast of the lower Chubut Valley. In 1881, the area became part of the Chubut National Territory of Argentina which, in 1955, became Chubut Province.