Time-resolved fluorescence decay measurements with pyrene as a probe have been employed to study the dynamics of entry and exit of several homologous N-alkylpyridinium ions (R-Py+) from cationic hexadecyltrimethylammonium chloride (CTACl) and acetate (CTAOAc) micelles over a wide range of concentrations of detergent and added common counterion salt (NaCl or NaOAc, respectively). The rate constants for entry of the N-alkylpyridinium ions into the micelle are insensitive to the alkyl chain length but increase with increasing concentration of detergent or added salt. In contrast, the rate constants for micellar exit of the N-alkylpyridinium ions are quite sensitive to the length of the alkyl chain attached to the pyridinium ion but relatively insensitive to salt or detergent concentration. Analysis of these results in terms of a simple pseudophase model suggests that the transition state for incorporation of amphiphilic colons such as the N-alkylpyridinium ions into ionic micelles is located just outside the Stern layer. These results provide a unified picture of the relationship between dynamics and selectivity of ion binding to ionic micelles.