Leslie is a brand of rotating speaker cabinets originally developed by Donald Leslie in the late 1930s and first marketed in 1941. Created to give the Hammond organ a more pipe-organ-like sound in domestic settings, Leslie's design used baffles and horns rotating around stationary speakers to produce a doppler-shifted, swirling tone that became inseparable from the sound of the Hammond organ in jazz, gospel, blues, rock, and progressive music. Early units were sold under names like Vibratone, Hollywood Speakers, and Crawford Speakers before Leslie standardized the branding through his company, Electro Music.

The classic Leslie cabinets — most notably the tube-amplified Model 122 (designed for Hammond consoles via a balanced connection) and the Model 147 (a universal-input variant) — pair a horn rotor for high frequencies with a 15-inch woofer firing into a rotating drum for the lows, switchable between slow 'chorale' and fast 'tremolo' speeds. Other notable models include the smaller 145 and 760, the combo-friendly 16/18/21 series, and modern designs like the solid-state 3300 and the Heritage 122H/142H reissues, alongside digital simulators such as the 2101.

Ownership of the Leslie name has passed through CBS, the Hammond Organ Company, and Suzuki Musical Instruments, which now produces Leslie cabinets alongside Hammond organs. The Leslie effect is so distinctive that it has been emulated by countless pedal and plugin manufacturers, and the cabinets themselves have been used by organists including Jimmy Smith, Booker T. Jones, Jon Lord, Keith Emerson, and Gregg Allman, as well as guitarists who route their signal through them for the characteristic rotary swirl.

Leslie has 35 products cataloged on Equipboard, including Keyboard Amplifiers, Combo Guitar Amplifiers, and Organ Accessories. Their gear is featured by 55 artists, with the strongest followings in Rock, Pop, and Metal. Notable users include Benmont Tench, Chris Copping, and David Gilmour. Most Leslie products sit firmly in the high-end, boutique range.