Fe-Ptthin-film alloys have been grown by electrodeposition at potentials positive to that required to deposit elemental Fe. X-ray diffraction studies indicate the formation of fine grained face centered cubic alloys, while Rutherford backscattering spectrscopy and energy-dispersive X-ray spectroscopy reveal substantial incorporation of oxygen in the FePt deposits. The Fe-Pt codeposition process is driven by the negative enthalpy associated with alloy formation. The experimentally determined relationship between alloy composition and the iron group underpotential was found to be in reasonable agreement with free energy calculations for the binary alloy system, based on thermochemical data. (C) 2004 The Electrochemical Society.