A study is made of the quenching by halide ions of the fluorescence of fluoranthene solubilized in CTAB micelles, using both steady-state and lifetime measurements. Stern–Volmer plots or plots of fluorescence decay rate against quencher concentration are non-linear, even under conditions of constant ionic strength. Only halide ions present in the Stern layer are effective in quenching and a relationship is derived between the concentration of ions present in the Stern layer and the total ion concentration using a multiple equilibrium model. Good agreement between theory and experiment is observed for the fluorescence decay rate and intensity as a function of total quencher ion concentration. The model shows that the quenching process is controlled by the quenching rate in the micelles and the association constant of the ions to the micelles. An increase in ionic strength leads to a decrease in the association constant and, owing to changes in micelle structure, it leads to an increase in the quenching rate in the micelle. The overall quenching effect is qualitatively dominated by the variations of the association equilibrium. The product of the micellar quenching rate constant and the number of active sites per micelle at an ionic strength of 0.3 mol dm^–3 is numerically identical to the quenching rate constant in water. This may indicate there being only one active site for quenching per micelle. The fluoranthene fluorescence lifetime is found to increase upon addition of chloride or fluoride ions, indicating that these ions are replacing the more strongly quenching bromide ion in the Stern layer. Iodide quenches fluoranthene fluorescence more strongly than bromide ion. Association equilibrium constants for halide ions with CTAB micelles are estimated.