A hairnet, or sometimes simply a net or caul, is a small, often elasticised, fine net worn over long hair to hold it in place. It is often worn by food service workers to prevent hair from contaminating the food. A snood is similar but a looser fit and with a much coarser mesh.

Evidence has been found of hairnets as far back as ancient Greece,^{[dead link]} further evidence are known from archaeological finds of Iron Age bog bodies from Denmark and Germany. Hairnets were worn from the 13th century onwards in Germany and England and are shown in illustrations from this period often worn with a wimple. They were made from extremely fine silk and edged with bands of either finger-weaving or tablet-weaving.

Ena Sharples, a character in the UK soap opera Coronation Street between 1960 and 1980, was famous for wearing a hairnet.

Hairnets are part of normal attire for female horse riders and are worn in most equestrian disciplines, including dressage, eventing, show jumping and hunting. Organisations such as the Pony Club encourage their young members to become accustomed to wearing hairnets when around horses, not only to ensure a neat and elegant appearance, but also to eliminate any danger of scalping should the rider fall off and the horse tread on loose hair.