Electrochemical micromachining (EMM) has emerged as a versatile process for machining and Surface Structuring of metallic materials for biomedical and microsystems applications. From a fundamental point of view EMM presents many similarities with electrochemical machining (ECMI) and electropolishing (EP) provided one takes into account the scale dependence of phenomena. In the present paper the role of mass transport, current distribution and passive films for shape control and surface smoothing is discussed and illustrated with examples. The usefulness of numerical simulation using simplified models is stressed. New developments in EMM of titanium are presented, including oxide film laser lithography permitting EMM on non-planar surfaces without photoresist and the fabrication of two-level and multi-level structures. Scale resolved electrochemical surface structuring of titanium leads to well-defined topographies on the micrometer and nanometer scales, which are of interest for biomedical applications. (C) 2003 Elsevier Science Ltd. All rights reserved.