Ferrous (iron-based) metals have widespread use throughout all branches of engineering but are particularly important in construction. Iron- and carbon-based alloys, that is cast iron and steel, are the principal forms of interest, and this chapter is primarily concerned with these, either for structural use in their own right or in the form of reinforcing or prestressing steel for concrete construction. We will also more briefly consider products formed by alloying with other elements, for example stainless steel.