A guernsey, or gansey, is a seaman's knitted woollen sweater, similar to a jersey, which originated in the Channel Island of the same name, sometimes known as a knit-frock in Cornwall.
The guernsey is the mainstay of Guernsey's knitting industry which can be dated back to the late 15th century when a royal grant was obtained to import wool from England and re-export knitted goods to Normandy and Spain. Peter Heylin described the manufacture and export of "waste-cotes" during the reign of Charles I. The first use of the name "guernsey" outside of the island is in the 1851 Oxford Dictionary, but the garment was in use in the bailiwick before that.
The guernsey came into being as a garment for fishermen who required a warm, hard wearing, yet comfortable item of clothing that would resist the sea spray. The hard twist given to the tightly packed wool fibres in the spinning process and the tightly knitted stitches, produced a finish that would "turn water" and is capable of repelling rain and spray.
The guernsey was traditionally knitted by the fishermen's wives and the pattern passed down from mother to daughter through the generations. While commercially available sweaters are machine knit, the final finishing of these machine-knit parts is completed by hand.
Through trade links established in the 17th century, the guernsey found favour with seafarers around the British Isles, and many coastal communities developed their own "ganseys" based on the original pattern. Whilst the classic guernsey pattern remained plain, the stitch patterns used became more complex the further north the garment spread, with the most complex evolving in the Scottish fishing villages.
Mary Wright argues that the use and wearing of guernseys throughout the British Isles for over a century and a half almost justifies the guernsey for qualification as a national costume. A guernsey from the Folk Museum Guernsey was included in the 2010 BBC project A History of the World in 100 Objects.