A muffler (known as a silencer in the United Kingdom and other areas) is a device for reducing the level of noise emitted by a machine, most commonly internal combustion engines. Mufflers often contain a series of baffles to cancel out the noise. They are a common piece of equipment for automobiles, usually slung under the rear of the car. Many diesel-powered semi trucks have larger mufflers mounted vertically behind the cab.

Catalytic converters also often have a muffling effect.

In the United Kingdom, a scarf is also known as a muffler.