There are two major varieties of Gamelan, Javanese and Balinese, and both use very similar orchestrations.
The gender is the most widely known instrument. It is a 14-keyed metallophone that elaborates on the main melody.
The saron is a smaller metallophone. It comes in three sizes and provides the main tune and rhythm.
The gambang is a wooden xylophone that shares the role of the gender.
The gongs provide the bass part and cue the other players to change the tune or beat. It is said that the soul of the gamelan lives within the largest gong.
The bonang is a series of kettle-shaped gongs on a frame. These provide an accompaniment throughout performances.
Over time other instruments have found their way into the gamelan orchestra. The suling (bamboo flute) and rebab (bowed instrument) are now part of many gamelans.