The links between catalytic and electrocatalytic hydrogenation processes are analyzed starting from the fundamental principles outlined in almost all works by Horiuti and Polanyi 70 years ago. It has been shown that the mechanistic picture based on the role of protontransfer step in processes taking place at the aqueous phase/catalyst (electrode) interface can be extended to a great number of electrocatalytic reductive transformations. Illustrative examples are shown including the reductive splitting of C-OH and C-Cl bonds in allyl position, the transformation of > C=O groups into -CH2- ones. The examples presented confirm the view that electrocatalytic studies, the application of electrochemical methods, constitute important contributions to the understanding of catalytic phenomena. (C) 2003 Elsevier Science B.V. All rights reserved.