Both classical multipolar interactions and the interaction-induced changes in intrinsic polarizability associated with van der Waals forces contribute to the long-range pair polarizability of atoms, oscillators, and dipolar rotors. The frequency-dependent nonlinear polarization of an isotropic system by the field due to the randomly fluctuating multipoles of neighboring systems and by an applied field determines the change in intrinsic polarizability induced in the system by van der Waals interactions. Frequency-dependent values for the mean-square fluctuating multipoles are obtained from the fluctuation–dissipation theorem. To lowest order (R−6) the dispersion contribution to the polarizability α(ω) of a pair of atoms A and B is related to an integral over imaginary frequencies iu of the symmetrized product (1+𝒫AB)γA(ω, iu,−iu)αB(iu), where γA(ω, iu,−iu) is a linear combination of the γ-hyperpolarizability tensor components of atom A and αB(iu) is the polarizability of atom B. By using a mean-frequency approximation, the dispersion contribution to the static polarizability of inert-gas atom pairs is found in terms of the known van der Waals coefficients CA6B, the static atomic polarizabilities, and static γ hyperpolarizabilities. To order R−6, the change in intrinsic polarizability is positive for hydrogen and inert-gas atom pairs, zero for pairs of isotropic Drude-model oscillators with vanishing dipole at the equilibrium geometry, and negative for pairs of rigid dipolar rotors.