Isothermal vapor-liquid equilibria were determined for two binary ionic liquid + water systems, from 323.3 to 368.2 K, and water mole fractions greater than 0.5. The ionic liquids used were 1-ethyl-3-methylimidazolium trifitioromethanesulfonate and 1-ethyl-3-methylimidazolium trifluoroacetate. In addition, predictive thermodynamic modeling of the vapor-liquid equilibrium was performed by correlating the nonrandom two-liquid,(39) universal quasi-chemical,(40) and electrolyte-NRTL41 models to previously measured excess enthalpy and infinite dilution activity coefficient data from the literature. For each of the systems studied at least two of the models provided adequate predictions of vapor pressure and water activity coefficients. The good predictions of vapor-liquid equilibria by these common activity coefficient models lead us to favor excess enthalpy and infinite dilution activity coefficient data over vapor-liquid equilibria data, since predictions of excess enthalpies from vapor-liquid equilibria are not satisfactory.