Nowadays to mitigate the greenhouse effect due to the use of fossil fuels it is necessary to identify a new highly efficient and environmentally friendly energy conversion technologies. The aim of this book is to present the main strategies for the development of high-performance membranes based on sulfonated aromatic polymers (SAP), in particular on cheap and versatile sulfonated poly(ether ether ketone) (SPEEK), for polymer electrolyte membrane fuel cells (PEMFCs) and, heating, ventilation, and air conditioning (HVAC) systems. The basic concepts of SAP, the synthesis and characterization of SPEEK, the membrane manufacturing techniques and the applications in the different fields mentioned above are summarized.