The self-association of alcohols and alkylphenols in hydrocarbon solutions, their association with extractants, especially with hydroxyoximes, and adsorption of modifiers at hydrocarbon/water interfaces in systems containing only modifiers and mixtures of modifiers and extractants are reviewed. Considering these processes, it is possible to successfully model metal extraction and to explain the modifier effects on the equilibrium and kinetics of metal extraction. The models for association of extractants with modifiers, their coadsorption at the liquid/liquid interfaces, and metal extraction with extractant-modifier mixtures are presented. Modifiers affect metal extraction both thermodynamically and kinetically by changing the concentration of the extractant active species and by blocking the interface that can be completely occupied by modifier-adsorbed molecules.