A metallophone is any musical instrument consisting of tuned metal bars which are struck to make sound, usually with a mallet.
Metallophones have been used in music in Asia for thousands of years. There are several different types used in Balinese and Javanese gamelanensembles, including the gendér, gangsa and saron. These instruments have a single row of bars, tuned to the distinctive pelog or slendro scales, or a subset of them. The Western glockenspiel and vibraphone are also metallophones: they have two rows of bars, in an imitation of the piano keyboard, and are tuned to the chromatic scale.
In music of the 20th century and beyond, the word metallophone is sometimes applied specifically to a single row of metal bars suspended over a resonator box. Metallophones tuned to the diatonic scale are often used in schools; Carl Orff used diatonic metallophones in several of his pieces, including his pedagogical Schulwerk. Metallophones with microtonal tunings are used in Iannis Xenakis' Pléïades and in the music of Harry Partch.