This paper provides two examples of computer simulation of interfacial phenomena, performed for the purpose of aiding the progress of experimental studies. In both cases, the modeling was performed by Monte Carlo methods, in conjunction with semi-empirical density functional type potentials. In the first example, simulations of compositional surface phase transitions in Cu-Ag alloys were performed. These simulations were very useful in guiding experiments away from (1 0 0)- to (I I I)-oriented Cu-Ag single crystals, where the sought-after transitions were eventually observed. In the second example, modeling was used to obtain quick estimates of the absolute values of Pb/Al interfacial energies. When measurements were eventually performed, the computed values were found to overestimate the measured Pb/Al(l 1 1) interfacial energy by about a factor of 3. Beyond those two examples, what we have learned from our own efforts at modeling alloy surface and interface phenomena with semi-empirical density functional type potentials, is that this type of modeling rarely produces quantitatively reliable predictions of compositions or energies. Nevertheless, some of the qualitative features of the predictions can often provide valuable insights for planning or interpreting experiments. (C) 2003 Elsevier Science B.V. All rights reserved.