The polymer electrolyte membrane is the heart of hydrogen fuelled Polymer Electrolyte Fuel Cells (PEFC) and methanol fuelled Direct Methanol Fuel Cells (DMFC). Membranes of sulfonated fluoropolymers are already commercially available. Important goals for research and development are for PEFCs an increased operating temperature without the need for additional humidification and for DMFC the reduction of methanol transport through the membrane. The use of non-fluorinated polymers aims at a reduction in membrane cost and environmental hazards. Membranes already in industrial product development are considered as well as novel membrane concepts in fundamental research.