The paper gives an introduction to this Special Issue and corresponding book ‘Electrochemical Micro- and Nano-System Technologies’ (Elsevier). Interdisciplinary aspects are demonstrated by microgalvanics, engineering, electrochemical materials science, electroanalysis and biology. Moreover, the continuous scaling down to molecular systems is described. Experimental parameters like topography, current densities, field strengths and hydrodynamics are characterised in double logarithmic plots. Types of reactions and materials properties determine the possibility of localisation and production rate. The EMT-number is introduced to differentiate maskless processes: delocalising 2D conditions (EMT>1) can be distinguished from localising 3D processes (EMT≪1). Nanoscopic localisation can be achieved using microelectrode arrays or micromechanical devices. Microscopic local elements play an important role in unwanted corrosion or intended structuring like phosphating. Examples of technical EMST applications are given and, for the case of phosphating, characterised in a flow-diagram and the Pourbaix-diagram.