Fluorescence spectroscopy has been utilized to determine the critical micelle concentrations (CMC) of anionic surfactants by external and internal probes and the results have been compared to those obtained by the surface tension method. The selection of anionic surfactants gave us the flexibility of having the probe within the surfactant molecule and having it reside at the palisade layer or in the micellar core. It is shown that the CMC value is not affected by the nature (whether part of the surfactant molecule or externally added) and location of the probe within the micelle. CMC values determined by surface tension and fluorescence techniques using external and internal probes agree quite well in linear alkylbenzene sulfonate (LAS) and secondary alkyl sulfonate (SAS) systems.