In many martial arts, each practitioner's level is marked by the color of the belt. The black belt is often the highest belt color one can attain, and proves a certain level of skill.

The black belt was 'invented' by Jigoro Kano, the founder of judo, who first devised the colored belt system and awarded the first black belts in the 1880s. He only used white and black belts, and it wasn't until the early 1900s that the colored belt system of awarding rank was created. Many modern martial artists, however, mistakenly believe that the belt ranking system is an ancient aspect of traditional martial arts. In the Japanese arts, the further subdivisions of black belt ranks are called dan grades where higher numbers means higher rank. The Korean arts have adopted the system, and even some Chinese arts nowadays have ranking systems with belt color as sign on rank.

One common idea concerning the tradition of belts claims that early martial artists began their training with a white belt, which eventually became stained black from years of sweat, dirt, and blood. However, there is no real evidence for this story, so it must for now be relegated to the status of myth. In fact, given standards of cleanliness common especially in traditional dojo, a student arriving with a bloodied or dirty uniform might well be thrown out in disgrace. In some arts and schools one has the opinion that the belt should not be washed; by doing that one would "wash away the knowledge" or "wash one's ki away." This might have something to do with the myth.

There is no way to compare belts and ranks between styles. In some arts, a black belt is quite easy to obtain while in others ten years of hard work is more of the rule than exception. It is a common belief that belts in budo arts are handed out more loosely in the West than in the motherland Japan, and indeed often a sign of bad schools is an abundance of black belt holders of low quality. However, in Japan rank often comes more or less automatically with time done and the black belt has little to do with the "master" level which westerners often think of when they hear the term "black belt".

One popular notion, posited in opposition to the "black belt as master" stereotype, is that a black belt indicates the wearer is competent in a style's basic technique. The black belt is thus seen not so much as an end, but rather as a beginning: the individual now "knows how to walk" and may thus begin the "journey." Of course, as noted above, rank is always a subjective matter.