A muffle furnace is a front-loading box-type oven or kiln for high-temperature applications such as fusing glass, ceramics and soldering and brazing articles.

A muffle fuenace in historical usage is a furnace in which the subject material is isolated from the fuel and all of the products of combustion, including gases and flying ash. After the development of high-temperature electric heating elements and widespread electrification in developed countries, new muffle furnaces quickly moved to electric designs. They are also used in many research facilities, for example by chemists in order to determine what proportion of a sample is non-combustible and non-volatile. Also, advances in materials for heating elements, such as molybdenum disilicide, can now produce working temperatures up to 1,800 degrees Celsius, which facilitate more sophisticated metallurgical applications.

The term muffle furnace may also be used to describe another oven constructed on many of the same principles as the box type kiln mentioned above, but takes the form of a long, wide, and thin hollow tube used in roll to roll manufacturing processes.

Both of the above-mentioned furnaces are usually heated to desired temperatures by conduction, convection, from electrical resistance heating elements. Therefore, there is no combustion involved in the temperature control of the system, which allows for much greater control of temperature uniformity and assures isolation of the material being heated from the byproducts of fuel combustion.