Over the last six years, we have published a series of papers developing a hydrodynamic model of thermodiffusion in liquids and liquid mixtures. Initial work focused on the movement of polymers dissolved in nonpolar solvents arising from the pressure gradient induced by asymmetry in polymer–solvent interactions as a result of the temperature-induced concentration gradient in the solvent. As that model was refined, we examined secondary effects of a macroscopic pressure gradient in the solvent, and finally extended our hydrodynamic approach to cross-diffusion and thermodiffusion in solvent mixtures. Application of the model is currently limited to non-ionic liquids, where molecular interaction energies can be estimated by Hamaker constants or similar parameters. In this paper we present the body of work as a whole, in order to ensure a consistent nomenclature and unify the model for application to liquid mixtures in general. To test the model, values of Soret coefficients for mixtures of toluene and n-hexane have been calculated using parameters in the literature.