This book explores PEM fuels cells and their potential in the energy transition. PEM fuel cells are electrochemical devices that can harness hydrogen energy and transform it into electricity.     The book is divided into three. The first section looks into the fundamentals of PEM fuel cells.   The second explores computational fluid dynamics (CFD) modeling of the dynamics of them. Every section of this book contains illuminating illustrations and informative tables. The final section provides bring together many practical applications and insightful recommendations, catering to both newcomers to the subject and existing fuel cell professionals.   This book acts as useful introduction and guide to PEM fuel cells for student engineers, experienced practitioners, and researchers.