The interdisciplinary field of electrochemical microsystem technologies (EMST) has a large impact on electrochemistry, electrochemical engineering, microengineering, material science, chemical analysis and its applications in biology and medicine. EMST include electrochemical reactions applied in microsystem technologies (MST) as well as MST applied in electrochemistry. Fundamental research refers to the scaling-down of reactions taking place in the mu m range. Control of electrochemical microreactions, their advantages and applications are discussed. The technical requirement of mass production presumes the scaling-up of the microreaction to a multifold macroscopic process. This is demonstrated for electrochemical processes, e.g, the LIGA process, as well as for MST for electrochemistry, e.g. the Foturan(R) technology. The final industrial process requires the realization of multistep processes which is illustrated with the phosphating process and the printed circuit board manufacturing us examples. Electrochemical microsystems are presented and classified by functionality and complexity.