A wind instrument consisting of a fipple like that of a recorder and a tube with a piston in it. It thus has an air reed like some woodwinds, but varies the pitch with a slide. Because the air column is cylindrical and open at one end and closed at the other, it overblows the third harmonic.

The slide whistle is most commonly used as a sound effect (such as in the sound tracks of animated cartoons, when a glissando can suggest something rapidly ascending or falling), but it is also possible to play melodies on the slide whistle.

The instrument became common in the 1920s when it was occasionally used in popular music and jazz as a special effect. Louis Armstrong switched over from his more usual cornet to the slide whistle for a chorus on a couple of recordings with King Oliver's band and his own Hot 5. At that time, slide saxophones, with reeds rather than a fipple, were also built. The whistle was also widely used in jug band music of the 1920s, such as Whistler's Jug Band.