In recent years the necessity for reduction of pollution, especially in large towns, has reinforced the interest in Polymeric Electrolyte Membrane Fuel Cells (PEMFCs) and a considerable effort to produce commercial FC vehicles is in progress. The main obstacles to their commercialization seem to be related to: (a) the high cost of both catalysts and proton conducting membranes [1]; (b) the low proton conductivity of the present membranes at low relative humidity (RH); (c) their high methanol crossover and (d) their instability at temperatures higher than about 80 8C when the RH values are higher than about 80 % (see later for details).In this situation, it is now becoming clear that an intense effort must be made to develop completely new types of membranes with the required characteristics. However, since it is not certain that new membranes for automotive PEMFCs better than the existing perfluorosulfonic acid ones will be found in the near future, efforts to improve the characteristics of known membranes by appropriate modifications must also be made.In this chapter, after a short discussion of the reasons why we need, especially for automotive applications, membranes of high conductivity and high stability in the temperature range 60-130 8C, we will be concerned with the above modifications and our attention will be mainly focused on composite membranes filled with nanoparticles of layered zirconium phosphate and phosphonates. After a short description of the structural features and proton conduction properties of these layered materials, the research performed on composite membranes based on non-perfluorinated and perfluorinated membranes filled with zirconium phosphate and zirconium metasulfophenylphosphonate nanoparticles and their preparation procedures will be summarized.The greater part of this research generally agrees on the positive effects of the above particles on the performance of fuel cells at medium temperatures. This can explain the interest for the use of these membranes in medium temperature PEMFCs for both automotive and stationary applications using hydrogen as a fuel. On the other Membranes for Energy Conversion. Volume 2. Edited by Klaus-Viktor Peinemann and Suzana Pereira Nunes