Early research on Proton Exchange Membrane (PEM) technology started in the mid-fifties at the beginning of the US space program. Proton conducting membranes were expected to advantageously replace corrosive acid electrolyte, the use of which limited the development of acidic fuel cells. The commercialisation of new membrane materials in the early seventies boosted R&D, mainly in the fields of water electrolysis and power generation using fuel cells. A survey of the various electrochemical applications of PEM cells is given in this paper. Emphasis is made on electrode structure in relation with the electrochemical performances of the cell.