The design, synthesis and some optical properties of hybrid organic-inorganic nanocomposites materials are presented. The properties that can be expected for such materials depend on the chemical nature of their components, but they also depend on the synergy of these components. Thus, the interface in these nanocomposites is of paramount significance and one key point of their synthesis is the control of this interface. These nanocomposites can be obtained by hydrolysis and condensation reactions of organically functionalized alkoxide precursors. Striking examples of hybrids made from modified silicon, tin and transition metal alkoxides are presented. Some optical properties (photochromic, luminescence, NLO) of siloxane based hybrids are also discussed.