This invention provides a membrane-mediated electropolishing process for polishing and/or planarizing metal work pieces. The work piece is wetted with a low-conductivity fluid. The wetted work piece is contacted with a first side of a charge-selective ion-conducting membrane, wherein the second side contacts a conductive electrolyte solution in electrical contact with a cathode. Current flow between the cathode and the work piece electropolishes metal from the work piece. This process can be used for both pure metals and alloys, and provides several significant advantages over conventional electropolishing processes. This invention also provides an apparatus useful in the membrane-mediated electropolishing process.