The theory and applications of electrochemical microfabrication technology are reviewed focusing on electrodeposition and dissolution processes. Electrochemical microfabrication offers some unique advantages over competing vapor phase technologies and therefore finds increasing use in the electronics and microsystems industries. The present paper discusses the underlying principles of electrochemical microfabrication processes. The important role of mass transport and current distribution is stressed and it is shown how numerical modeling contributes to the present understanding of critical process parameters. The application of electrochemical microfabrication technology in the electronics industry is illustrated with selected examples.