The article begins with a brief presentation of the strategic importance of the hydrogen evolution reaction in various fields; this is followed by a discussion of its reversibility and of the factors on which reversibility depends. Adsorption of hydrogen atoms is a necessary step that depends on the interaction of metal surfaces with solvents. Thus, a correlation is found between M-H bond strength and hydrophilicity of metal surfaces. This point is discussed with the help of voltammetric curves for platinum-group metals. Besides being adsorbed, hydrogen atoms can also penetrate beneath the surface, thus affecting the adsorption energy on the surface. Hydrogen evolution is often accompanied by cathodic poisoning owing to the presence of metallic impurities. Ways to minimize this are discussed. The three most popular mechanisms of the electrode reaction for hydrogen liberation are discussed and kinetic parameters reported. The effect of the coverage of the electrode with the intermediate (H ad) is illustrated in detail. The effect of the nature of the electrode material (in electrocatalysis) is discussed using the so-called volcano curves depicting the dependence of the activity on M-H bond strength. A detailed analysis of electronic and geometric factors in electrocatalysis is also carried out. Finally, the findings of a survey of the most active materials in acidic and alkaline solutions are presented.