Polymer nanocomposites for optical applications require high optical transparency at high filling ratios of nanoparticles. The nanoparticles provide optical functionality but unfortunately have a strong tendency to aggregate in polymer matrices leading to strong turbidity and reduced optical transmission, particularly at high filling ratios. We report a general route to nonaggregated highly filled, optically transparent polymer nanocomposites. It is based on using nanoparticles that have been coated with polymers forming spherical brushlike layers providing thermodynamic miscibility with the polymer matrix over the complete range of nanoparticle volume fractions. The polymers are attached via a versatile ligand exchange procedure which enables to prepare a wide range of optically transparent polymer nanocomposites up to weight fractions of 45%. This is demonstrated for a broad range of metal and semiconductor nanoparticles in optically transparent polymer matrices relevant for selective light/UV absorption, photoluminescence, and high/low refractive index polymer materials.