Diffraction studies of nonstoichiometric compounds have revealed a diverse range of diffuse scattering effects due to the short-range order induced by atom and vacancy substitution or by atomic displacements. In this paper, diffuse neutron and X-ray scattering data and electron diffraction data on short-range order in nonstoichiometric compounds are discussed. It is shown that the redistribution of non-metallic atoms and structural vacancies in disordered nonstoichiometric carbides, nitrides, and oxides produces diffuse intensity maxima in diffraction patterns, as does the redistribution of mutually substitutable metallic atoms in the solid solutions of nonstoichiometric compounds before long-range order sets in. A discussion is given of whether the cluster model of transition state is adequate for describing diffuse scattering intensity profile in a nonstoichiometric compound with substitutional short-range order. Flat extended diffuse scattering regions observed in the diffraction patterns of ordered phases and not passing through reciprocal lattice sites are discussed and shown to be due to the appearance of atomic displacement waves in the material.