This book provides readers with a comprehensive understanding of fuel cells, including their fundamental principles, technical features, and practical applications. Fuel cells, as an ideal way of hydrogen utilization, are of great significance in promoting the hydrogen society. The aim of this book is to introduce the basics of various fuel cells and to provide a detailed description of some important research fields in PEMFC, such as catalysts, systems, and degradation. The book is intended for undergraduate and graduate students who are interested in energy conversion technology, researchers investigating hydrogen energy, and engineers working on renewable energy or other energy storage applications.