Abstract Mass transfer across interfaces greatly determines the kinetics of heterophase polymerization. All molecules in the system can cross any interface as long as they possess enough energy to overcome barriers such as interfacial tension, chemical potentials, etc. Two main groups of mathematical approaches have been used to model mass transfer: macroscopic deterministic and molecular stochastic. Macroscopic modeling may use fundamental laws, thermodynamic expressions and empirical or semi‐empirical equations. Molecular models are based on the discrete character of nature and include stochastic simulation, BD or MD. Special emphasis is placed on the most relevant molecular transfer processes observed in free‐radical emulsion polymerization. magnified image