EFAB (Electrochemical FABrication) is a new micromachining technology targeted at the rapid, automated batch fabrication of an unlimited variety of high-aspect-ratio metallic microstructures. By applying the principles of Solid Freeform Fabrication to the manufacturing of microstructures, EFAB provides nearly arbitrary, truly 3-D geometry. EFAB exploits `Instant Masking' - a new high-speed in-situ selective plating technique - to quickly, repeatably, and precisely deposit an unlimited number of layers of material. EFAB makes possible economical prototype and short run production of microstructures using inexpensive desktop equipment, yet is scalable to mass production. By generating layers using electrodeposition at low temperature, EFAB makes feasible the manufacture of extremely complex microstructures that are deposited over and electrically integrated with standard foundry-processed ICs.