Thermodynamic and kinetic principles which govern the uptake of nonionic, hydrophobic organic chemicals by sediments in aqueous systems are summarized. Sorption onto organic-rich sediments can be modeled as a process where the hydrophobic compound partitions into the organic matter associated with the sediments analogous to the partitioning in the octanol water system resulting in a linear free energy relationship between the two partition coefficients. The influence of dissolved organic matter can be accounted for by considering a binding isotherm between the hydrophobic solute and dissolved macromolecules. Adsorption at the mineral-water interface becomes important when the adsorbate contains polar functional groups and/or when the adsorbate contains quite small concentrations of organic matter. Sorption can require more than a month to reach equilibrium for highly hydrophobic compounds, but can be adequately described by a radial diffusion model accompanied by the retarding influence of sorption.