In this chapter, the key role of fuel cells and regenerative fuel cell technologies, in the future energetic scenarios based on renewable energy sources, is described. The fuel cell technology is reviewed; its working principles are summarized and mathematically described by means of a simple analytical model. It is found that the limits of fuel cell competitiveness can be overcome only through a specific design of its key component materials: the electrolyte and the electrocatalyst. Examples of material design research achievements are reported for both fuel cells and regenerative fuel cells. © Springer Science+Business Media Dordrecht 2014. All rights are reserved.