Surfactants are used in increasingly large quantities in a number of consumer and industrial products. Adsorption of surfactants to surfaces of suspended particles affects their removal in waste treatment plants. Adsorption of surfactants on particles affects their distribution, fate, and effects in natural waters. Experiments were conducted to study the properties of surfactant (charge and structure), solution (H(+)), (Ca(2+)), and (Na(+)), and sorbent (e.g., organic carbon and cation exchange capacity) that affect adsorption. The surfactants studied included dodecylpyridinium, homologs of linear alkylbenzenesulfonates, and homologs of 'alcohol ethoxylates' (monoalkyl ethers of poly(ethylene glycol)). Adsorption isotherms were determined for a set of five soils and sediments. Isotherms determined with aqueous-phase concentrations in the submicromolar range were all nonlinear and were described well by the Freundlich equation. The adsorption energies reflected a combination of hydrophobic, electrostatic, and specific chemical interactions. The results of the authors' study indicate that the properties of sorbent and solution that control adsorption are different for different classes of surfactants. The results are discussed relative to adsorption mechanisms and surfactant speciation in natural waters.