Isothermal titration calorimetry was used to examine the energetics of surfactant aggregation in the absence and presence of hydrophobically modified alkali-soluble emulsion (HASE) polymers. The binding behavior of SDS onto several model HASE polymers with C-1, C-8, C-12, C-16, and C-20 hydrophobes was investigated. A 0.1 wt % HASE polymer solution was titrated with a 0.1M SDS solution. For all the SDS/polymer systems, pronounced endothermic differential enthalpic curves are observed. Thermodynamic parameters such as enthalpy and entropy change of aggregation confirm that the process for the binding of SDS to the hydrophobic junction is entropy-driven. The Gibbs energy of binding of SDS onto the model polymers increases from -2.9 kJ/mol for C-1 hydrophobe to -4.2 kJ/mol for C-20 hydrophobes. The critical aggregation concentration and the negative enthalpy of aggregation decrease with increasing polymer hydrophobicity.