Compartmentalization refers to the physical confinement of reactants within confined space of nanosize dimensions and is a concept exploited by nature for the synthesis of various biomolecules. In the field of synthetic polymer chemistry, compartmentalization mainly refers to the "segregation effect" with two species located in different nanoparticles being unable to react and the "confined space effect" with two species in the same particle reacting faster for a smaller nanoparticle size. Compartmentalization kinetic effects on conventional radical (emulsion) polymerization kinetics have been relatively well understood for some time, whereas the influence in reversible deactivation radical polymerization (RDRP) is considerably more complex and remains an active area of research. This Perspective provides a concise overview of compartmentalization kinetic effects at sufficiently low particle sizes (e.g., below 100 nm) on conventional radical polymerization, RDRP, cross-linking polymerization, and nonradical polymerization reactions. It is demonstrated that the phenomenon of compartmentalization can be exploited as a means of exerting influence on the polymerization kinetics without manipulating the fundamental chemistry of the polymerization, provided that sufficient attention is paid to interphase exit and entry mass transfer events.