Theoretical and experimental aspects of alloy plating for surface treatment of metals are reviewed from an electrochemical and materials science point of view. The importance of mass transport and current distribution for alloy deposition studies is pointed out. The consequences for experimental cell design are mentioned and the usefulness of the recently developed rotating cylinder Hull (RCH) cell is illustrated. Theoretical aspects of alloy plating are discussed based on mixed potential theory. Three types of behavior are distinguished : non-interactive systems, charge transfer coupled systems and mass transport coupled systems. The usefulness of quantitative modeling for improving the theoretical understanding of multi-parameter processes such as alloy deposition is stressed. Finally, different factors influencing the microstructure of electrodeposited alloys and their engineering performance are presented.