It is now possible to investigate in detail metal/liquid interfaces by solid-state NMR under external potentiostatic control, in the presence of an electrolyte, by using the electrochemical NMR (EC NMR) technique. This permits the determination of the electronic properties of electrodes and of adsorbates as well as the study of the surface diffusion of adsorbates. The method also provides useful information on the dispersion of platinum fuel cell catalysts, on electrochemically generated sintering effects, and on the electronic effects caused by the presence of different surface adatoms. In general, EC NMR provides information on the following: (1) metal surface E-f LDOS, the chemical significance of which is that these describe the local frontier orbitals of the metal surface; (2) adsorbate structure/bonding details, such as 5sigma and 2pi* E-f LDOS, metal-surface bonding to atoms in the adsorbate, and even bond lengths; (3) rates and activation energies for surface diffusion; and (4) electrode potential effects on the electronic properties of the electrochemical interface, as seen by both metal and ligand NMR. We review here, therefore, the current status of the EC NMR technique, together with its applications to investigating the metal/electrolyte interface.