The aggregation of surfactant molecules in the presence of macromolecules is treated by considering that the latter modify the microenvironment of the former by changing the interfacial tensions between the hydrocarbon core of the micelle and solvent and between the headgroups of the surfactant molecules in the micelles and solvent. Conditions are identified under which the critical micelle concentration of the free aggregates, formed in the volume of solution free of macromolecules, is smaller, greater, or equal to the critical micelle concentration of the aggregates bound to the macromolecules. The model considers cases free of specific interactions as well as cases in which specific interactions do occur and leads to the conclusion, among others, that the lack of change in the critical micelle concentration when a nonionic polymer is added to the solvent does not exclude the formation of aggregates bound to the polymer chains.