Adding to the efforts spent to establish localized electrochemical deposition as a standard fabrication process, this paper presents an experimental investigation and theoretical modeling of shape formation of high aspect ratio columns and lines fabricated by localized electrochemical deposition. The proposed model suggests that transport of depositing ions leading to deposit formation is dominated mainly by migration forces. The deposition model is verified by numerical simulation which utilizes electric field calculation by a boundary element method and a progressive boundary update approach to determine the evolution of deposition profiles. Simulation results are compared against images of copper columns obtained at different formation stages during the deposition process. Both results are in agreement, which demonstrates the potential and capabilities of the proposed model and simulation procedures as an analysis tool to aid in characterizing the deposition process and resulting structures, as well as the understanding of the dynamics and factors influencing object formation in localized electrochemical deposition. (C) 2003 The Electrochemical Society.