Various synthetic protocols were used to prepare several classes of polysiloxane-silica filler systems. The structures of these fillers and their interactions with the polysiloxane matrices were studied using small-angle X-ray and neutron scattering. In addition, the mechanical properties of the composites were characterized using equilibrium stress-strain isotherms in elongation. The results indicated that manipulation of the chemical reactions used to generate the filler can lead to a wide range of complex structures and unusual properties. Some of the observed mechanical properties were correlated with information on the composite structures and on elastomer-filler interactions.