A kiln is a type of high temperature oven used in a variety of processes, from the roasting of hops for beer to the manufacture of ceramics. A kiln may also be called a furnace, depending on the industry in which it is used in. Most people differentiate a kiln from an oven by the extremely high temperatures which it reaches. These temperatures require a kiln to be lined with specialized material which will not fail in heat which may exceed thousands of degrees.

Materials put in a kiln may be dried, hardened, or directly burned, depending on how much they are heated. Many grains are kiln dried, as is timber which is classically dried to cure it. Other materials such as ceramics may be hardened with the use of a kiln, which actually changes the chemical composition of the clay. A kiln may also be used to burn things, reducing wood to charcoal, for example.

Many specialized kilns are designed to meet a particular need. The designs of these kilns factor in the ways in which they will be used. A ceramic kiln, for example, usually has a series of adjustable shelves to fit ceramics on, and it will be designed to fall within a particular temperature range. Cremation kilns are designed specially for processing human bodies, while lumber kilns are intended for use in curing lumber. Different types of kilns are built for processing limestone, or use in industrial manufacture.

When objects are heated in a kiln, the process is called firing. Typically, the objects must be loaded very carefully before a firing, so that they use the heat in the kiln efficiently and they do not explode. The kiln is usually brought to temperature slowly, so that the objects inside are not shocked, and it is cooled equally slowly. Once cooled, the objects can be removed from the kiln.

Natural gas is a common source of fuel for kilns. Some kilns may use electricity, propane, or even wood. Wood firing is a classical choice for ceramics, when artists want to practice ancient techniques of ceramics manufacture. During the firing process, the outside of the kiln may get extremely hot, so caution around the kiln is advised. The temperature is monitored with the use of tools like pyrometric cones and thermometers. Since small temperature differences can have a dramatic impact on the goods being fired, it is extremely important to keep an eye on the temperature of a kiln so that the firing is not ruined.