High temperature solid oxide fuel cells (SOFCs) offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. These fuel cells provide many advantages over traditional energy conversion systems including high efficiency, reliability, modularity, fuel adaptability, and very low levels of NOx and SOx emissions. Furthermore, because of their high temperature of operation (similar to 1000 degreesC), natural gas fuel can be reformed within the cell stack eliminating the need for an expensive, external reformer. Also, pressurized SOFCs can be successfully used as replacements for combustors in gas turbines; such hybrid SOFC-gas turbine power systems are expected to reach efficiencies over 70%. This paper reviews the materials and fabrication methods used for the different cell components, and discusses the performance of cells fabricated using these materials; it also discusses the materials and processing studies that are under investigation to reduce the cell cost. Finally, the paper summarizes the recently built power generation systems that employed state-of-the-art SOFCs. A new design SOFC that combines the seal-less feature of tubular cells and a flattened air electrode with integral ribs is also described; this new design has a shortened current path and hence lower cell resistance and higher power output than tubular cells. (C) 2000 Published by Elsevier Science BN.