The definition of sustainability is still under discussion, but it is becoming increasingly clear that present practices of energy supply and distribution are causing severe environmental pressures, and that they cannot be continued indefinitely. The fuel cell has been undergoing rapid development and is now at a stage immediately prior to commercialisation for a number of markets. It is expected to be economically competitive with many other energy conversion technologies within the next 5 years. However, introduction of the fuel cell may also speed the economic introduction of emissions-free energy carriers such as hydrogen, linking directly to renewably generated electricity. Hydrogen could be used as a form of energy storage in cases where electricity demand and supply were not matched. The fuel cell would then be complementary to, rather than competitive with, renewable generation technologies. Ultimately, the fuel cell, in both its high and low-temperature derivatives, could become one of the pillars of a future sustainable energy system.