Ferro alloy is an alloy of iron with some element other than carbon. Ferro alloy is used to physically introduce or "carry" that element into molten metal, usually during steel manufacture. In practice, the term ferro alloy is used to include any alloys that introduce reactive elements or alloy systems, such as nickel and cobalt-based aluminum systems. Silicon metal is consumed in the aluminum industry as an alloying agent and in the chemical industry as a raw material in silicon-based chemical manufacturing.

The ferro alloy industry is associated with the iron and steel industries, its largest customers. Ferro alloys impart distinctive qualities to steel and cast iron and serve important functions during iron and steel production cycles. The principal ferro alloys are those of chromium, manganese, and silicon. Chromium provides corrosion resistance to stainless steels. Manganese is essential to counteract the harmful effects of sulfur in the production of virtually all steels and cast iron. Silicon is used primarily for deoxidation in steel and as an alloying agent in castiron. Boron, cobalt, columbium, copper, molybdenum, nickel, phosphorus, titanium, tungsten, vanadium, zirconium, and the rare earths impart specific characteristics and are usually added as ferro alloys.