The Hammond organ is an electric organ which was designed and built by Laurens Hammond in April 1935. While the Hammond organ was originally sold to churches as a low-cost alternative to the pipe organ, it came to be used for jazz, blues, and to a lesser extent rock music and gospel music.

In imitation of a pipe organ, with its banks of pipes in multiple registers, the Hammond Organ used additive synthesis of waveforms from harmonic series to generate its sounds. As in Thadeus Cahill's earlier Telharmonium, the individual waveforms were made by mechanical "tonewheels" which rotated beneath electromagnetic pickups.

Because the waveforms are produced by mechanical tonewheels rather than electronic oscillators, original Hammond organs are considered to be electric rather than electronic organs.

A defining feature of the Hammond organ was the use of "drawbars" to mix the component waveforms in varying ratios. Other features added to Hammond organs included an electromechanical vibrato. The distinctive "key click" that was originally a design flaw rapidly became part of the "Hammond sound", which modern imitations of the Hammond organ faithfully reproduce. Accurate imitation of the Hammond sound with electronics is difficult, because the phase relationship between tonewheels is difficult to replicate.

Speakers made by Leslie were widely used with the Hammond organs, though at first, Leslie was a competing company that Hammond sought to drive out of business. The Leslie speakers had a rotating component that produced a vibrato effect. Soon, the Leslie became a de facto component of any Hammond setup wishing to produce that signature "growling" sound.

The model B-3 was, and still is, the most sought-after model, though the C-3 differs only in cosmetics. Hammonds can be divided into two main groups: the 'Console' models such as the B-3, C-3 or A-100 which have two 61 note manuals and the smaller 'Spinet' models that have two 44 note manuals such as the L-100 and the M-100. Most Hammond organs do not have a full AGO pedalboard, something that was done originally for cost and size reasons.