An electronic organ is an electronic keyboard instrument which was derived from the harmonium, pipe organ and theatre organ. Originally, it was designed to imitate the sound of pipe organs, theatre organs, band sounds, or orchestral sounds. Today, it has developed into three or more types of instruments:
The immediate predecessor of the electronic organ was the harmonium, or reed organ, an instrument that was very popular in homes and small churches in the late 19th and early 20th centuries. In a fashion not totally unlike that of pipe organs, reed organs generated sound by forcing air over a set of reeds by means of a bellows, usually operated by constantly pumping a set of pedals. While reed organs had limited tonal quality, they were small, inexpensive, self-powered, and self-contained. The reed organ was thus able to bring an organlike sound to venues that were incapable of housing or affording pipe organs. This concept was to play an important role in the development of the electric organ.