A kiln is an oven that is used for hardening, burning, or drying anything. Kilns have been used for converting wood into charcoal and are used to heat dried clay objects in order to make them hard and durable in a process referred to as firing. Kilns are also used for cremation. They are also used to dry green lumber so that the lumber can be used immediately.

A kiln is required to come to a high temperature, and so the design of the ovens normally focuses on insulation, and the ability to add fuel over a course of time. Care must be taken not to heat the kiln too much as clays are made of alumino and magnesium silicates which will degrade under high temperatures leaving oxides of aluminium, magnesium and silica, which can form glass at high temperatures.

Kilns have been made for as long as there has been pottery and items made of clay. The technology is thus very old. Early examples of kilns found in the United Kingdom, include those made for the making of roof-tiles during the Roman occupation. These kilns were built up the side of a slope, such that a fire could be lit at the bottom, and the heat would rise up into the kiln.

See also limekiln.