  When immiscible liquids are subject to electric fields interfacial forces
arise due to a difference in the permittivity or the conductance of the
liquids, and these forces lead to shape change in droplets or to interfacial
instabilities. In this Topical Review we discuss recent advances in the theory
and experiments of liquids in electric fields with an emphasis on liquids which
are initially miscible and demix under the influence of an external field. In
purely dielectric liquids demixing occurs if the electrode geometry leads to
sufficiently large field gradients. In polar liquids field gradients are
prevalent due to screening by dissociated ions irrespective of the electrode
geometry. We examine the conditions for these "electro prewetting" transitions
and highlight few possible systems where they might be important, such as in
stabilization of colloids and in gating of pores in membranes.
