We show in this letter that nonlinear interactions between noncollinear elastic waves can be analyzed by using the well‐known mathematical formalism of wave propagation in periodic media, which leads to a set of coupled amplitude equations much like those found in the optoacoustic interaction case. The behavior predicted from these equations for isotropic media is well consistent with results known for Bragg diffraction in anisotropic media. The conditions for an experiment using a lead molybdate crystal are derived. By using the optoacoustic analogy, some device applications may be thought of and the scope of the present work may be extended to cover interactions involving elastic surface waves.