The key to utilizing graphite as a platelet nanoreinforcement is in the intercalation and exfoliation of this material to the nano level as individual graphene sheets and the dispersion in polymers to achieve percolation. Theoretical predictions for percolation and mechanical properties will be discussed. Experimental results will be presented in which thermoset and thermoplastic matrix composites have been fabricated with graphite nanoplatelets at concentrations up to ~10 volume percent. The nanocomposites made with these nanographite platelets have significantly higher moduli that nanoclay platelet reinforced composites with little reduction in composite tensile strength compared to the neat matrix.