The expected end of the “oil age� will lead to increasing focus and reliance on alternative energy conversion devices, among which fuel cells have the potential to play an important role.  Not only can phosphoric acid and solid oxide fuel cells already efficiently convert today fossil fuels, including methane, into electricity, but other types of fuel cells, such as polymer electrolyte membrane fuel cells, have the potential to become the cornerstones of a possible future hydrogen economy. Featuring 21 peer-reviewed entries from the Encyclopedia of Sustainability Science and Technology, Fuel Cells offers concise yet comprehensive coverage of the current state of research and identifies key areas for future investigation.  Internationally renowned specialists provide authoritative introductions to a wide variety of fuel cell types, and discuss materials, components, and systems for these technologies. The entries also cover sustainability and marketing considerations, including comparisons of fuel cells with alternative technologies.