A polymeric nanoparticle composition is provided. The nanoparticle may be of a core/shell configuration with an interphase region connecting the core and the shell. The mean average diameter of the polymer nanoparticles may be less than about 250 nm. The size, composition, and/or configuration of the interphase region may be varied to achieve desired physical and/or chemical properties of the resulting polymeric nanoparticles, and of the compositions into which the nanoparticles are compounded.