A first principles model is herein presented aimed at simulating the initial stages of pulsed electrochemical micromachining, EC mu M, a technique introduced by Schuster et al. over a decade ago (Schuster et al. Science 2000, 289, 98-101). Our strategy is based on finding solutions to the equations that govern mass transport of all solution phase species coupled to Poisson's equation for the electrostatic potential in solution subject to boundary conditions that relate the potential across the tool vertical bar electrolyte and workpiece vertical bar electrolyte interfaces to the rates of heterogeneous electron transfer. This complex problem including its moving boundary aspects was solved using COMSOL without assuming a priori a capacitive element. The results obtained for a Pt tool and Cu workpiece employing conditions similar to those specified by Schuster et al. in their original work were found to be in good agreement with those obtained experimentally. (C) 2013 The Electrochemical Society. All rights reserved.