We extend the scattering approach to electrical conduction in quantum coherent structures to investigate the frequency dependence of the current response to time-dependent voltages. In structures with low transmission, the leading order in frequency response is determined by sample specific quantum capacitances. In structures with high transmission the leading order is determined by a kinetic inductance. In zero-dimensional systems these coefficients can be expressed in terms of the Wigner-Smith matrix. We discuss two experiments which measure an L/R time and an RC-time. In the single channel limit the charge relaxation resistance of a mesoscopic capacitor is universal equal to half a resistance quantum.