This article explores the legality of balisongs (also known as butterfly knives) in Japan. Balisongs have a long history in Japan, with some believing they were first introduced by Portuguese traders in the 16th century. Regulations on balisong are governed by the Police Law which states that any knife with a blade longer than 5 cm (about 2 inches) must be registered with police authorities if one wishes to carry it outside their home or place of business. Other laws include banning carrying weapons while intoxicated and using them for anything other than self-defense. Owning a balisong legally does not require registration provided its blade length does not exceed 5 cm (about 2 inches), however carrying it outside requires registration depending on where you live.