Redox stabilities or electrochemical windows (EWs) of ionic liquids (ILs) commonly are measured through linear sweep voltammetry by using the ILs as electrolytes with solid electrodes. The present report demonstrates how the electrode materials affect these measurements. As model systems, two ILs, 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, are examined using Au, Pt, Ta and Glassy Carbon electrodes. The EWs are determined using voltammetry, and the reactive features of the surfaces are probed with impedance spectroscopy. It is shown that these EWs depend on the work function of the electrode, while the interfacial reactions are largely dictated by the IL properties. (C) 2009 Elsevier B.V. All rights reserved.