The review is devoted to the main aspects of the formation of crystalline nuclei (nucleation) during electrochemical crystallization of metals and outlines the current state of both theory and experiment in this field. It is emphasized that electrochemical deposition of metals is both a useful model system and a rapidly developing method for obtaining new materials. Theoretical provisions related to the thermodynamics of nucleation and the kinetics of formation and growth of individual crystals and mass crystallization are presented, taking into account diffusion and overlap processes with further cluster growth. The methods of electrochemical and structural studies are briefly considered, as well as the results of studying the electrochemical nucleation and growth of a number of metals on surfaces of various nature.