Mixed polysaccharide-surfactant systems have broad applications.A review of the underlying polymer-surfactant association in bulk is given.While ionic surfactants bind broadly to polysaccharides, nonionics only do so if the polymer has a lower polarity and can interact by hydrophobic interactions.Water-soluble polysaccharides, which have hydrophobic groups, form physical cross-links, hence their important use as thickeners.The rheological behaviour is strongly influenced by various cosolutes; especially strong effects are due to surfactants and both a decrease and an increase in viscosity can occur.This can be referred to mixed aggregate phenomenon and a simple model is presented.