Fundoshi (ふんどし/褌) is a traditional Japanese undergarment for men and women, made from a length of cotton.
Before World War II, the fundoshi was the main form of underwear for Japanese men and women. However, it fell out of use quickly after the war with the introduction of new underpants to the Japanese market, such as briefs, boxer briefs and panties. Nowadays, the fundoshi is mainly used not as underwear but as festival (matsuri) clothing at Hadaka Matsuri or, sometimes, as swimwear.