A quantitative discussion of the combined influence of three electro mechanical effects: piezoelectricity, flexoelectricity, and electrostriction in solids is provided for acoustic absorption and gain. While piezoelec tricity occurs in noncentrosymmetric materials only, flexoelectricity and electrostriction exist in all materials. Two important new results are dem onstrated: 1) the possibility to realize acoustic gain in all materials (cen trosymmetric and noncentrosymmetric) when the acoustic Cherenkov condition is fulfilled, and 2) realization of acoustic gain in the presence of a strong dc electric field, even when the Cherenkov condition is not fulfilled, in the case of strong crosscoupling between piezoelectricity, flexoelec tricity, and electrostriction. A simple analytical expression for the acoustic dispersion relation is derived for the combined effect of piezoelectricity, flexoelectricity, and electrostriction. At lower frequencies, the piezoelectric effect dominates for inversionasymmetric materials. At high frequencies (≈>1 MHz) flexoelectricity becomes increasingly important and eventually provides a major mechanism for gain and absorption in barium titanate (BaTiO 3). In the presence of strong electric fields (≈>1 MV m −1), electrostric tion provides a dominant isolated contribution to absorption/gain in BaTiO 3. Strong coupling between the three electromechanical contributions determines the total absorption/gain coefficient.