Highly monodispersed ZnO nanoparticles (NPs) have been synthesized in polyol medium. The control on crystal size was attempted at 180°C by monitoring the heating rate of reacting solutions and the cooling rate (quenching) at the end of the reaction time. The possibility to promote crystal growth by heterogeneous nucleation was also evaluated; in this approach, pre-synthesized 5-nm pure ZnO nanocrystals were used as seeds in fresh Zn-polyol solutions at suitable seeds/ZnO w/w ratios. As-synthesized samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Fourier Transform Infrared spectroscopy (FT-IR), Absorbance (UV-vis) and Photoluminescence spectroscopy (PL). XRD measurements confirmed the formation of well crystallized ZnO-wurtzite with absence of secondary phases in both seeds and grown crystals. FT-IR analyses evidenced the presence of organic moieties on the surface of the nanoparticles that are associated to the functional groups of polyol by-products; these adsorbed species would have prevented particles from aggregation. PL measurements (excitation wavelength 345 nm) reveled that a tuning in the emission bands of ZnO NPs can be achieved through synthesis conditions and crystal size. HRTEM measurements evidenced the formation of bare ZnO NPs of 2 nm, 6 nm, 20 nm and clusters of small nanocrystals.