The concept of wave hierarchies in the Whitham's sense is generalized to hierarchies of second order wave operators. Based on Mindlin's model of microstructured solids, the scaling procedure is described and the corresponding hierarchical equation derived which includes two wave operators. It is shown that waves in the Cosserat' medium are described by a similar hierarchical equation. These results are generalized to a multiscale case (a scale within a scale) and to nonlinear media. It is shown also how to construct hierarchies for waves in elastic ferroelectrics. The results obtained by Scott for hierarchies in thermoelasticity are presented in the similar framework. Finally, the cases with first order wave operators are described.