This book provides a comprehensive platform for the research, scientific and educational communities working on electrocatalysis. It covers water electrolysis from different fields of catalysis research, deals with the fundamentals and critically discusses the precise and correct use of evaluating parameters and their calculation for a fair evaluation. Readers find an analysis to probe the origin of different bottlenecks in water electrolysis and scientific methods to enhance the electrode selectivity with high intrinsic activity, effective mass and electron transfer ability, abundant active sites with super hydrophilicity-aerophobicity characteristics and structural, mechanical and chemical stability with high corrosion resistance.