Publisher Summary This chapter discusses structure and properties of metals and alloys. With metals and alloys one is interested in the form of the solid or crystal orbitals, Ψ. On the electronic structure of metals and alloys and its relation to electron spectroscopies, the most important quantity is most probably the density of states, N(E). Hydrocarbons form a large variety of adsorbed intermediates on the surface of metals and alloys. The chapter presents Engel–Brewer theory of metals and alloys. This theory has a number of features that are similar to the ideas of Pauling: directed valencies, an important role of hybridization of orbitals on atoms constituting the metal, widely changing valencies and the omnipresent electron pairs. The Engel–Brewer theory has also been applied to problems of the stability and crystallographic structure of alloys, in particular to structures of some intermetallic compounds. Such compounds are formed when a metal on the left-hand side of the periodic table (that is, a metal with almost empty d-orbitals) is combined with a metal on the right-hand side, where elements have several d-orbitals with paired d-electrons. Some results of the theory of chemisorption on metals and alloys are presented.