A theoretical description for the dynamic surface properties of binary surfactant mixtures containing (i) two insoluble surfactants, (ii) two soluble surfactants, or (iii) one insoluble and one soluble surfactants was developed, We showed that previously reported expressions for surface dilational modulus do not correctly account for surface compositional dependence, New expressions, which take into account composition effects explicitly, for the frequency-dependent dilational visco-elastic modulus (based on diffusion-controlled adsorption) for these three systems were obtained, In the limit of high surface deformation frequencies, the surface dilational elasticity epsilon(0) for the binary mixtures considered here reduces to epsilon(0) = -(partial derivative sigma/partial derivative Gamma(1))(Gamma 2T)Gamma(1) - (partial derivative sigma/partial derivative Gamma(2))(Gamma 1,T)Gamma(2).