Amorphousfilms are understood to be solids in which the postulated atomic arrangement shows no crystallike ordering beyond a few neighbors. The structure of such amorphousfilms is usually characterized by a diffuse x-ray or electron-diffraction pattern, consisting of a few broad rings or halos, and by a lack of contrast in transmission electron micrographs. However, very small, randomly oriented crystallites of <30 Å in diameter will also produce diffraction patterns which are qualitatively similar to those exhibited by amorphous solids. The theories of small-angle scattering and large-angle diffraction are discussed in terms of the structural disorder in the solids (electron-density fluctuations, atomic distributions, particle sizes) and are applied to the investigations of the structure of amorphousalloyfilms, such as liquid-quenched Fe–P–C and Pd–Si alloys, electrodeposited Ni–P alloys, and vapor-quenched Cu–Mg and Ag–Cu alloys.