Electrochemical studies at a carefully characterized Pt(111) electrode surface are yielding useful insights into atomic, ionic and molecular electrochemistry at interfaces. Reviewed here are studies of the chemisorption of the common polar aprotic solvent acetonitrile (CH3CN) at a Pt(111)surface. Electrosorption of CH3CN under typical electrolytic conditions from CH3CN electrolyte, CH3CN aqueous electrolytic solutions and CH3CN vapor was investigated by high-resolution electron energy-loss spectroscopy (HREELS, vibrational spectroscopy), Auger electron spectroscopy (AES, elemental analysis), low-energy electron-diffraction (LEED, structure/symmetry probing) and linear potential scan cyclic voltammetry (cv, exploration of electrochemical maturity). The results indicate that a chemisorbed layer is for-med from CH3CN liquid, vapor and typical aqueous solutions. The chemisorbed layer consists of a mixture of species related to CH3CN and acetamide (CH3CONH2), contains about theta = 0.15 molecules per surface Pt atom is stable in vacuum and in solution over a wide range of electrode potentials, is replaced only slowly by other strong adsorbates such as iodide and lacks long-range order in the absence of anions such as iodide. Related studies are exploring ionic absorption, organic molecular adsorption and electrodeposition of metallic monolayers. A brief overview and references are included.