Jiu-jitsu is know as “the gentle art” and is practiced by millions world wide. While this grappling style originated in Japan, the Gracie family of Brazil made many technical changes while popularizing it in Vale Tudo no-holds-barred matches and through the UFC. While many train for sports and competitions, it is one of the most effective combat and self-defense styles ever developed.
Much is written about Brazilian jiu-jitsu (BJJ). Take a look at this article from The Gracie Academy for a nice overview.
This video provides a nice history as well.