Brazilian Jiu-Jitsu (BJJ) is a martial art and combat sport that focuses on grappling and especially ground fighting with the goal of gaining a dominant position from which to force an attacker to submit. The system is based a modified version of traditional Japanese Jujutsu called "Jiu-do" which is based on the idea of soft overcoming the hard. In other words, smaller, weaker person using leverage and proper technique to defend themselves against a bigger, stronger assailant. BJJ can be trained for self defense, sport grappling tournaments (gi and no-gi) and mixed martial arts (MMA) competition. Sparring and live drilling play a major role in training, and a premium is placed on performance, especially in competition.

The art began when Mitsuyo Maeda, a master of Japanese jujitsu and judo/Jiu-do, which was the changing of jujutsu training methods to a non-lethal degree and also where Helio Gracie got the word "jiu" from. Maeda immigrated to Brazil where he taught his system to Carlos Gracie, who passed it on to his younger brother Helio. The brothers trained many of their sons, who now carry on the family tradition today. The Gracie family continued to develop the system throughout the 20th century, often fighting vale tudo matches (precursors to modern MMA), during which it gained its focus on ground fighting and refined its techniques.

Brazilian Jiu-Jitsu came to prominence in the United States when Royce Gracie won the first, second and fourth Ultimate Fighting Championships in the earlier 90s. It has since become a staple art for many MMA fighters and is largely credited for bringing wide-spread attention to the aspect of ground fighting. Sport BJJ tournaments continue to grow in popularity worldwide and have given rise to no-gi submission grappling tournaments, such as ADCC.

The art is sometimes referred to as Gracie Jiu-Jitsu (GJJ) but this name is trademarked by Rorion Gracie and specifically refers to the style taught by him and his selected teachers. Other members of the Gracie family often call their style by personalized names, such as Charles Gracie Jiu-Jitsu or Renzo Gracie Jiu-Jitsu, and similarly, the Machado brothers call their style Machado Jiu-Jitsu (MJJ). While each style and its instructors have their own unique aspects, they are regarded as variations of Brazilian Jiu-Jitsu.