There is increasing research interest in producing hydrogen through polymer electrolyte membrane (PEM) electrolysis as a way of converting renewable energy to hydrogen fuel. This book provides comprehensive coverage of the fundamentals and applications of PEM electrolysis and reviews state-of-the-art technologies and challenges related to each of the components. In addition, the text addresses failure analysis and describes available failure diagnostic tools while providing future research directions to assist scientists and technology developers in bringing commercially viable PEM electrolysis systems to fruition.