Various strategies, which lead to the manipulation of molecules adsorbed at surfaces by means of external electric fields are proposed. First, explicitly time-dependent laser radiation is considered. For the example system NH3-Cu(111), a two-dimensional adiabatic model and nuclear wave packet propagation are adopted to study the desorption of NH3 by "vibrational ladder climbing" and "above threshold desorption," both driven by a series of ultrashort infrared pulses. Another strategy makes use of static fields and leads to "field desorption," for which isotope effects and higher-order contributions to the molecule-field interaction are addressed in some detail. We also study the reverse process to desorption, adsorption. Starting with (i) the elastic and inelastic scattering of "randomly oriented" (molecular beam) ammonia molecules off the surface, we then consider (ii) the scattering of static-field aligned molecules and, finally, (iii) the laser-induced adsorption (LIA) of gas-phase molecules by stimulated emission of photons.