Particle nucleation is the forcing function in emulsion polymerization reactions and as Such it plays a significant role in the development of most of the properties of the final latex. The locus Of nucleation in emulsion polymerization remains a contentious issue. Recent developments in the spectroscopy of emulsions strongly suggest that the locus of particle nucleation is a population of small nano-droplets of size range between 30-100 nanometers in diameter. These nano-droplets are generated independently of the rate of initiator decomposition and appear to be functions only of the emulsification conditions. In this paper the simulation studies leading to the identification of the nano-droplet population are described. The theoretical evidence suggesting that the nano-droplets are the main loci of particle nucleation is presented and along with the recommendations for the experimental work. (c) 2006 Wiley Periodicals, Inc.