Brazilian jiu-jitsu  (BJJ; Portuguese: jiu-jitsu brasileiro) is a martial art, combat sport, and a self-defense system that focuses on grappling and especially ground fighting. Brazilian jiu-jitsu was formed from Kodokan Judo ground fighting (newaza) fundamentals. Brazilian jiu-jitsu eventually came to be its own art through the experimentations, practices, and adaptation from the Judo knowledge of Japan, combined with Luta Livre of Brazil and Wrestling from America.

BJJ promotes the concept that a smaller, weaker person can successfully defend against a bigger, stronger assailant by using proper technique, leverage, and most notably, taking the fight to the ground, and then applying joint-locks and choke-holds to defeat the other person. BJJ training can be used for sport grappling tournaments (gi and no-gi) and mixed martial arts (MMA) competition or self-defense. Sparring(commonly referred to as "rolling") and live drilling play a major role in training, and a premium is placed on performance, especially in competition, in relation to progress and ascension through its ranking system.

Since its inception in 1882, its parent art of Judo was separated from older systems of Japanese ju-jutsu by an important difference that was passed on to Brazilian jiu-jitsu: it is not solely a martial art, it is also a sport; a method for promoting physical fitness and building character in young people; and, ultimately, a way (Do) of life.