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Herein, we report the aggregation behavior of catanionic mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in solution and at the air/water interface obtained by the Langmuir–Blodgett (LB) technique. We employed Fourier transform infrared spectroscopy, in situ phase-contrast inverted microscopy, scanning electron microscopy, and atomic force microscopy to characterize the systems in solution, at the air/water interface, and in LB films. We found spherical vesicles at the SDS/CTAB ratio of 35/65 in aqueous solution and an ordered aggregated morphology called surface micelles at SDS/CTAB ratios of 35/65 to 65/35 at the air/water interface. Other mixtures (SDS/CTAB = 90/10, 10/90) were found to contain mostly disordered aggregated microstructures. An in situ time-dependent study of surface micelle formation at the air/water …