This chapter contains sections titled: Polymers Can Induce Surfactant Aggregation Attractive Polymer–Surfactant Interactions Depend on Both Polymer and Surfactant Surfactant Association to Surface Active Polymers Can be Strong The Interaction between a Surfactant and a Surface Active Polymer is Analogous to Mixed Micelle Formation Phase Behaviour of Polymer-surfactant Mixtures Resembles That of Mixed Polymer Solutions Phase Behaviour of Polymer–Surfactant Mixtures in Relation to Polymer–Polymer and Surfactant–Surfactant Mixtures Polymers May Change the Phase Behaviour of Infinite Surfactant Self-assemblies There are Many Technical Applications of Polymer–Surfactant Mixtures DNA is Compacted by Cationic Surfactants, Which Gives Applications in Gene Therapy Bibliography