Koryū (古流?) is a Japanese word that is used in association with the ancient Japanese martial arts. This word literally translates as "old school" (ko--old, ryū--school) or "traditional school." Koryū is a general term for Japanese schools of martial arts that predate the Meiji Restoration (the period from 1866 to 1869 which sparked major socio-political changes and led to the modernization of Japan). While there is no "official" cutoff date, the dates most commonly used are either 1868, the first year of the Meiji period, or 1876, when the Haitōrei edict banning the wearing of swords was pronounced.

The systems of Japanese martial arts that post-date the Meiji Restoration are known as gendai budō. The most well known of these arts include judo, kendo, some schools of iaidō, and aikido. These newer systems are commonly valued as sports or arts for self-improvement. The koryū systems of martial arts, however, are commonly far more revered as they are considered the teachings of the true Japanese martial arts, because they were formed from Japan's feudal military culture.

The koryū systems of the Japanese martial arts often contain both unarmed and armed fighting techniques. Within these ancient systems several different weapons are commonly taught to the students of the these arts.