Fuel cell technology has gained increasing attentions as it provides a promising sustainable approach for facing the existing energy crisis and environmental concerns. Fuel cell based power generation has been proposed to be applied in transport and distributed energy supply. However, the development of fuel cell is still in its early stages, which must overcome several issues before its commercial application, such as cost, process efficiency and working stability. This book provides a general picture on the development of fuel cells. In particular, two representative fuel cells, (ie: PEM fuel cells and solid oxide fuel cells), were reviewed in detail. The book is intended to serve as a reference for both researchers and postgraduate students within the field of chemical/biological fuel cells.