In recent years, Polymer Electrolyte Fuel Cells (PEFC) have attracted much attention due to their potential as a clean power source for many applications, including automotive, portable and stationary devices. This resulted on a tremendous technological progress, such as the development of new membranes and electro-catalysts or the improvement of electrode structures. However, in order to compete within the most attractive markets, the PEFC technologies did not reach all the required characteristics yet, in particular in terms of cost and durability. This book focuses on the recent research progresses on the fundamentals understanding of the materials degradation phenomena in PEFC, for automotive applications. On a multidisciplinary basis, through contributions of internationally recognized researchers in the field, this book provides a complete and comprehensive critical review on crucial scientific topics related to PEFC materials degradation, and ensures a strong complementary between experimental and theoretical analysis (experimental accelerated aging methods in ex-situ and in-situ conditions, stability properties of nanoparticles, structural and physicochemical characterization methods of degradation, detailed theoretical modeling, elementary mechanisms, nano-electrocatalysts and carbon support behaviour under realistic operation conditions...) and preparation techniques (technologies of nano-electro-catalysts, membranes and carbon support elaboration...) with several practical applications for both the research and the industry communities.