One of the earliest electronic music instruments. Originally known as the etherphone, it is controlled without physical contact by the player. It is named after its Russian inventor, Léon Theremin, who patented the device in 1928.

The instrument's controlling section usually consists of two metal antennas which sense the relative position of the player's hands and control oscillators for frequency with one hand, and amplitude (volume) with the other. The electric signals from the theremin are amplified and sent to a loudspeaker.