Aqueous suspensions of cellulose nanocrystals can be prepared by acid hydrolysis of the biomass. Due to their nanoscale dimensions and intrinsic physicochemical properties, these nanoparticles are promising renewable biomaterials. The high mechanical properties and reinforcing capability of these nanoparticles make them attractive for the processing of high performance nanocomposites. The main problem is related to the homogeneous dispersion of these nanoparticles within the polymeric matrix. Because cellulose nanocrystals are obtained as aqueous suspensions, water is the preferred processing medium. However, new strategies are envisaged to broaden the polymeric matrices that can be reinforced with these nanoparticles and avoid the liquid medium processing way. This paper reviews the different processing techniques of cellulose nanocrystals reinforced polymer nanocomposites focusing on the challenging melt processing technique.