Radical desorption is one of the most important physical processes influencing the kinetics of free-radical emulsion polymerization. Desorption of any molecule from a polymer particle can only take place if the molecule reaches the particle surface during its random diffusion through the polymer phase. For doing this the molecule must survive all possible competitive reactions taking place simultaneously inside the particle. Once at the surface it must also overcome a certain energy barrier in order to leave the particle. This energy barrier is determined mainly by the difference in the chemical potential of the molecule between the particle and the continuous phase (including interfacial tension effects) and by additional barriers such as the presence of a stabilizer layer. In this molecular picture of the desorption process all molecules inside the polymer particle can desorb from the particle at a rate determined by its energy barrier and diffusion coefficient. It is for this reason that desorption of the smaller and more hydrophilic molecules is predominant. In this paper we propose the use of Brownian dynamics (BD) algorithms for simulating the desorption of radicals from polymer particles and estimate the corresponding desorption rate coefficients. The results obtained in simple systems are found to be in very good agreement with the rate coefficients of desorption determined theoretically. For more complex systems, such as core-shell particles, nonspherical particles, hollow particles, or particles with a gradient in monomer concentration, BD simulations open the possibility to obtain easy, reliable estimations of the desorption rate coefficients, which are difficult to obtain using the experimental or theoretical methods currently available. This article is also intended to be a comprehensive and critical review of the different available theories of radical desorption in emulsion polymerization.