The ondes Martenot or ondes musicales is an early electronic musical instrument. It is played with a keyboard or by moving a ring along a wire, creating "wavering" sounds similar to a theremin. A player of the ondes Martenot is called an ondist.

An electronic musical instrument or electrophone is a musical instrument that produces sound using electronic circuitry. Such an instrument sounds by outputting an electrical, electronic or digital audio signal that ultimately is plugged into a power amplifier which drives a loudspeaker, creating the sound heard by the performer and listener.