The paper tries to make a critical inventory of Ionomers, free of fluorine or fluorine less, which can be used as alternatives to Nafion (R) in polymer electrolytes fuel cells, as Ionomer is indisputably one of the main bolts of these technologies. All the Ionomer families are discussed, with their main advantages and drawbacks, in particular in terms of their possible industrial scale-up. Special attention has been paid to the discussions about the choice of the ionic functions and that of polymeric backbones of the Ionomers, with regard to the required electrochemical proper-ties and also to their thermomechanical behaviour. It has been emphasized that a global approach of the polymer electrolytes is essential to progress. This must involve (i) a control of the syntheses up to the pilot scale, (ii) thorough characterizations, (iii) attention to the membrane and the MEA assembly and (iv) durability investigations, including post-mortem characterizations. (c) 2005 Elsevier B.V. All rights reserved.