The subject of this book is geometric integrators for differential equations with highly oscillatory solutions, including oscillation-preserving integrators, continuous-stage ERKN integrators, nonlinear stability and convergence analysis of ERKN integrators, functionally-fitted energy-preserving integrators, exponential collocation methods, volume-preserving exponential integrators, global error bounds of one-stage ERKN integrators for semilinear wave equations, linearly-fitted conservative/dissipative integrators, energy-preserving schemes for Klein–Gordon equations, Hermite–Birkhoff time integrators for Klein–Gordon equations, symplectic approximations for Klein–Gordon equations, continuous-stage modified leap-frog scheme for high-dimensional Hamiltonian wave equations, semi-analytical exponential RKN integrators,long-time momentum and actions behaviour of energy-preserving methods.The new geometric integrators are applied to problems with highly oscillatory solutions from sciences and engineering.