The propagation and instability characteristics of small signal interfacial waves are examined for charged fluids in planar, cylindrical, and spherical equilibrium. The configurations discussed are electrohydrodynamic versions of the classic fluid mechanical problems of the Rayleigh‐Taylor instability with superposed charged layers, of interfacial capillary oscillations of charged liquid cylinders, and extensions of Rayleigh's and Bohr's analysis of charged spherical drops under surface tension. In these geometries, a liquid which is either electrically perfectly conducting with surface charge or perfectly insulating and polarizable with volume charge is immersed within a uniformly charged perfectly insulating region. Using a general set of relations for perturbation field and flow variables defined for a “prototype” layer, the dispersion characteristics for these two limits are easily derived using interfacial boundary conditions and are compared in each of the geometries. For all cases, the system tends to be stabilized if the charges in each region are of opposite sign.