The emulsion polymerization of styrene has been studied using several surface chemical techniques. Evidence has been obtained from dye adsorption, latex morphology, and microelectrophoresis studies, which indicate that two quite different mechanisms can operate, depending on the process conditions. Use of a water-insoluble initiator appears to favor micellar nucleation, whereas persulfate initiator tends to produce latex via homogeneous nucleation in the aqueous phase. An atomic force microscope adapted to measure surface forces was used to study the interactions between polystyrene in water and surfactant solutions. The strong hydrophobic attraction observed presents a likely explanation for the buildup of latex particles in the homogeneous nucleation process.