An Indonesian percussion instrument. It is the largest of the bronze gongs in the Javanese and Balinese gamelan orchestra and the only large gong that is called gong in Javanese. Unlike the more well known largely flat Chinese gongs (chau gongs) or tam-tams, Indonesian gongs have fixed, focussed pitch and are dissimilar to the familiar crash cymbal sound.

A gong ageng is circular, with a conical, tapering base of a diameter smaller than the gong face, with a protruding polished boss where it is struck by a padded mallet. Gongs with a diameter as large as 135 cm (53 inches) have been created in the past, but gongs around 80 cm (31 inches) are more common. 

There is at least one large gong in each gamelan, but two are common and older gamelans may have three or more. The gong ageng usually has its own name, which may be bestowed upon the entire set of instruments. It is considered the most important instrument in a gamelan ensemble - the soul or spirit of the gamelan is said to live in the gong.