Rank in Judo are ranked in ascending numerical order. The ninth ("kudan") and tenth degree black belt ("jūdan") and, theoretically, those higher, have no formal requirements. Only 15 individuals have been promoted to the rank of Kōdōkan 10th dan. On January 6, 2006, three individuals were promoted to this rank simultaneously: Daigo Toshirō, Ichirō Abe, and Ōsawa Yoshimi. This is the most ever at the same time, and the first in 22 years. No one has ever been promoted to a rank higher than 10th "dan", but in theory the Judo rank system is not limited to 10 degrees of black belt. The
Judo were called ; and only those of 4th "dan" or higher were called "judoka". (The suffix , when added to a noun, means a person with expertise or special knowledge on that subject). A judo teacher is called . The word "sensei" comes from "sen" or "saki" (before) and "sei" (life) – i.e. one who has preceded you. In Western dojo, it is common to call an instructor of any "dan" grade "sensei". Traditionally, that title was reserved for instructors of 4th "dan" and above. Judo practitioners traditionally wear white uniforms called or . sometimes abbreviated in the west as