Surface tension and neutron reflection measurements have been used to study the micellization and interfacial adsorption of ternary surfactant mixtures containing sodium dodecyl sulfate (SDS), n-dodecyl-N,N-dimethylaminoacetate (C(12)Betaine or C12B), and n-dodecyl-beta-D-maltoside (C12M). Critical micelle concentrations (cmc) for the ternary mixtures are compared with values predicted using a multicomponent extension to the pseudophase separation model for nonideal mixing. Although the observed cmcs may be up to 50% different from those predicted, the errors resulting from inadequacies in the binary model mean that the results are the same within error. Values of the surface excesses at the air/solution interface at the cme were determined directly using neutron reflection and isotopic substitution. They are found to be quite different from those predicted using the binary interaction parameters determined by surface tension. However, if the apparent, binary interaction parameters obtained from directly measured compositions in the binary systems are used, the agreement between prediction and experiment is much improved. This suggests that prediction of the properties of ternary surfactant mixtures may be relatively straightforward once mixing in binary mixtures is properly characterized.