In this book, the harmonic oscillations of gas- filled axisymmetric acoustic cavities are considered. A mathematical model is developed to account for the full nonlinear behavior of the gas oscillations. The equations are cast in a weighted residual form which can be solved provided that the exact mode shapes are known. The model is proved to be accurate in capturing the formation of shock waves at large excitations. However, it is solvable only for resonators with simple geometries. A finite element model is developed based on the weak form of the governing equations in order to solve resonators of complex geometries. The model is integrated with the dynamics of axisymmetric piezoelectric bimorphs that are used in actuation. The validity of the coupled model is validated experimentally and against the predictions of a commercial finite element packages based on linear acoustic equations. Close agreement is obtained between theory and experiment indicating that the developed model can be confidently used in the design of axisymmetric acoustic resonators.