Much research has been undertaken in methanation of CO and CO² and, as such, methanation is widely employed in industrial applications for complete conversion (removal) of CO and CO². As a novel deep CO abatement process, research into selective CO methanation is occurring.This book analyses the vast existing research on CO and CO² methanation to find key issues to perform CO methanation selectively and demonstrates the process experimentally in an actual reactor scale. It also offers a focus on a new deep CO removal process in polymer electrolyte fuel cells (PEFCs), including selective CO methanation catalysts and reactors, along with conventional CO abatement processes such as water gas shift and preferential oxidation of CO (PROX). In addition, related CO removal techniques and current fuel cell systems are presented. The book is ideal for graduate students, fuel cell researchers, chemical engineers and chemists with an interest in the field.