Judo employs a "Dan" (degree) and "Kyu" (grade) ranking system to indicate levels of skill. Judo was the first martial art to adopt the ranking systems used in Go and Shogi. These "Dan" and "Kyu" concepts were subsequently combined, resulting in the current ranking system. This system is also used in Kendo, Karate, and Kyudo (Japanese Archery).
Judo sets a rank according to the level of skill. "Kyu" rankings are expressed in descending order (the lower the rank number, the higher the skill level), and "Dan" rankings are expressed in ascending order (the higher the rank number, the higher the skill level).
Judo belt colors vary according to the "Dan" or "Kyu" ranking. The widely known "black belt" is allowed only for "Dan" class practitioners.
Although colors are classified as shown above, a black belt is often worn even by Judo practitioners with ranks of 6th Dan or higher. Originally, it was customary to use Judo belts without ever washing them. Because the belts therefore became soiled (blackened) with repeated practice, the black belts became associated with strength, and were worn by "Dan" rank practitioners.
Dan / Kyu ranks and methods of promotion
Although Judo practitioners normally begin from the lowest rank of 10th Kyu, those of junior high school age or older may petition to begin from the 3rd Kyu. Moreover, a beginning practitioner may proceed directly to the 1st Kyu if sanctioned by a Judo judge. Promotion tests for the lower Kyu ranks consist of winning a required number of bouts. Practitioners of the 1st Kyu rank are registered with the Judo Association, and are eligible to receive tests for promotion to the "Dan" black-belt class.
Testing for promotion to the "Dan" class consists of a combat test, a form (Kata) test, and a written test. Practitioners who pass all three of these tests receive a 1st Dan ranking, and are allowed to wear a black belt. However, only those aged 14 or older are eligible for the 1st Dan ranking. Because those seeking promotion to the "Dan" class must win a required number of bouts, they must often return to the dojo (training hall) several times over a period of several days. In addition to their level of skill, those seeking promotion must also have engaged in the required "years of study" which is set for each rank.