A technique where chakra kneaded inside the body is converted into fire, and expelled from the mouth in a massive orb of roaring flame. The scope of the attack is altered by controlling the volume of chakra that is mustered. The released flames will engulf their target, and leave a crater on the ground's surface. The fireball is normally blown through a ring made by the thumb and index finger of the user. However, Sasuke Uchiha and Itachi Uchiha are seen doing this technique without making a ring over their mouth.
According to Kakashi Hatake (in the anime Part II), the Fire Release: Great Fireball Technique was originally created by the Uchiha clan, becoming one of their favorite moves with which they became very adept. The Uchiha clan also uses the Fire Release: Great Fireball Technique as a "coming of age" technique. This technique apparently requires more than average chakra reserves and most Genin should not be able to do this technique.