The Ondes Martenot (or Ondes-Martenot or Ondes martenot or Ondium Martenot or Martenot or ondes musicale) is an early electronic musical instrument with a keyboard and slide invented in 1928 by Maurice Martenot, and originally very similar in sound to the Theremin. The sonic capabilities of the instrument were subsequently expanded by the addition of filter banks and switchable loudspeakers. The instrument is especially known for its eerie wavering notes produced by the thermionic valves that produce oscillating frequencies.
The Ondes Martinot has been used by many composers, most notably Olivier Messiaen. He used it in many of his works, such as the Turangalîla Symphony and the Trois Petites Liturgies de la Presence Divine. Other composers included Pierre Boulez, Edgar Varese, Darius Milhaud, Arthur Honegger and Maurice Jarre.
The instrument was frequently used in soundtracks for horror and science fiction movies, and is still used from time to time. Its uses include Lawrence of Arabia (1962), Billion Dollar Brain (1967), and Amélie (2001). On television Barry Gray frequently used it in his scores for Gerry Anderson's series.