Koryū-bujutsu are the old martial schools of the samurai warrior arts which were founded in feudal Japan and are transmitted directly from master to student in an unbroken lineage up to the present day. The koryū (traditional martial art schools) served the purpose of educating the bushi (samurai) in the arts and strategies of war, which were necessary for them to survive and succeed on the battlefield as well as in duels. But the teachings are not only restricted to the martial techniques, they also contain reihō, the traditional etiquette, which teaches how to behave, move and act according to the customs of feudal Japan, as well as tetsugaku. Tetsugaku literally translated means philosophy. The philosophy educated the samurai ethically in relation to the arts of war and their everyday life. All those aspects combined have the goal to bring out a warrior with an undefeatable mind and body.
In comparison, gendai-budō, the modern Japanese martial arts such as kendō, jūdō, aikidō, iaidō or jōdō which were developed after 1868 (Meiji restoration) and the simultaneous abolishment of the feudal system of clans and bushi (samurai), set their focus on a sportive approach. They adjusted themselves to the western world and culture, rather than to continue the original teachings and traditions of the bushi and traditional feudal Japanese culture, like the koryū (traditional martial art schools) do and thus lost the connection to the reality of fighting.
The different koryū are rigidly and hierarchically structured. A koryū is solely led by its sōke (head of the school), who is responsible for making decisions, leading and representing the school, passing on the teachings to the next generation and to issue grading licenses.
In some schools the sōke is not actively practicing, but he still leads the school as nominal head and authorizes the various legitimate shihanke (master) lines of his school, if there exist some side lines next to the main line. A sōke can also hand over the school to an active shihan of his or another line. This former shihan becomes the new sōke and continues the main line of a school which is then passed down through his family until another family change may happen. There are also a couple of schools which don’t have the sōke/iemoto system at all. In those schools the highest ranking shihan leads the ryūha or the different teaching lines are completely independent from each other.
The grading licenses in koryū are traditionally awarded in form of makimono (scrolls) in which the secrets of the schools are transmitted. There are no dan/kyu grades or coloured belts and patches in traditional koryū, as those are modern inventions. Also koryū are normally not members of international federations and associations. They act independently with the sōke as the leader, who is supported by the shihan of his school. The same occurred during the feudal era of Japan and this tradition is kept alive ever since.
There are currently around one hundred koryū still extant. They all managed to survive for hundreds of years and passed their teachings on, from generation to generation. Though there are no sportive tournaments between the various ryūha (schools), it sometimes happens that a high ranking member of a school challenges a master of another tradition to a duel. However, this is generally only allowed to high ranking and very advanced members of the schools.
Koryū are considered an important part of the history and culture of Japan. The above mentioned structure and tradition makes it possible for every student, who is training in one of them, to be able to study the chosen school exactly the same way as it was done back in feudal Japan.
This is just a very short overview, which should explain roughly what koryū-bujutsu is. It is important to understand that each koryū has a characteristic culture and identity, most probably very different from each other.