Brazilian Jiu Jitsu is a martial art developed by the Gracie family of Brazil. It's roots lie in the arts of Judo and traditional Jujutsu. Where BJJ differs dramatically is in its focus on ground fighting. Through a variety of chokes and joint locks, a BJJ practitioner is able to control and defeat his opponent without causing serious or lasting harm.
Unlike many other martial arts, progression in BJJ is not measured by the ability to memorize a complex series of moves or forms, but rather by one's ability to apply the art in live sparring. It is for this reason, amongst others, that BJJ is highly effective in real world self-defense settings. A deep knowledge and understanding of BJJ is also imperative for anyone who is attempting to be succesful in Mixed Martial Arts.