Large advances have been made in the application of cathodic stripping voltammetry (CSV) to the determination of trace elements in the environment. A monomolecular layer of complexes on a mercury electrode is allowed to adsorb directly from aqueous solution during the pre-concentration step, which is followed by measurement of the reduction current by means of a potential scan to more negative potentials. The entire adsorbed layer is reduced during the potential scan, causing the voltammetric measurement to be very sensitive to low dissolved analyte concentrations. A review is given of the ligands used to measure trace elements in aqueous solution, and of the elements which can be determined. The adsorption step of what are in fact fairly soluble (in water) complexes is controlled by a mixture of effects related to π-orbital electrons and electrostatic interactions. The high sensitivity to the analyte is a result of the efficient (complete) electrochemical reduction of the monomolecular layer of adsorbed material. Although not a multi-element technique, CSV is superior to other analytical techniques in the automated monitoring of trace elements in natural waters including sea water, and in the study of speciation. An added advantage is related to the comparatively low cost and simplicity of the instrumentation.