New and more efficient energy conversion systems are required in the near future, due in part to the increase in oil prices and demand and also due to global warming. Fuel cells and hybrid systems present a promising future but in order to meet the demand, high amounts of hydrogen will be required. Until now, probably the cleanest method of producing hydrogen has been water electrolysis. In this field, solid oxide electrolysis cells (SOEC) have attracted a great interest in the last few years, as they offer significant power and higher efficiencies compared to conventional low temperature electrolysers. Their applications, performances and material issues will be reviewed.