The adsorbed layer structure of tetradecylpyridinium, hexadecylpyridinium, heptadecafluorodecylpyridinium, and tetradecyltriethylammonium chloride and their mixtures on mica has been determined by AFM imaging. In addition, the composition of the mixed adsorbed layers has been measured, showing a significant surface enrichment of the pyridinium. surfactants, particularly the partially fluorinated species. Shape transitions in the adsorbed layer are correlated with surface and bulk compositions and explained by consideration of the adsorption mechanism.