A preliminary study has been made of the mechanism by which metals burn. Experiments have been carried out with wires of aluminium, iron, magnesium, molybdenum, titanium and zirconium in oxygen and oxygen + nitrogen mixtures. The rate of propagation of the combustion zone along the wire is dependent upon the oxygen pressure in the atmosphere, suggesting that combustion is largely controlled by gaseous diffusion through the atmosphere. Some of the factors influencing the mode of burning and the reaction rates have been studied, and the temperatures attained under the given experimental conditions have been measured. The mode of burning is determined by the relative melting and boiling points of the metal and its oxide. Metals with low boiling points, such as aluminium and magnesium, burn in the vapour phase. Metals which have high boiling points, but which melt readily, burn at the surface of a molten oxide + metal mixture, provided the oxide also melts readily but has a high boiling point. Iron and titanium are examples of such metals. If, as with zirconium, the metal has a high boiling point and possesses a refractory oxide, a solid oxide film, which slows the reaction, can be formed on the metal surface. Metals such as molybdenum, which form oxides that readily sublime burn at the surface of the metal. Colour temperatures attained during the burning of iron, titanium and zirconium in oxygen were found to be higher the greater the pressure of oxygen. The temperatures were in the range 2600 to 3600 $^\circ$K, and were highest for the metal with the greatest heat of oxidation when measured per gram of oxygen consumed. The burning of a metal sphere to a molten oxide + metal mixture in a convection-free monomolecular gas has been treated theoretically. The variation of combustion temperature with oxygen pressure predicted by the theory agrees satisfactorily with that obtained experimentally.