Book excerpt: Materials with nanometer size particles exhibit unique chemical and physical properties. In particular, nanocomposite materials, composed of nanometric metal and metal oxide particles embedded in vitreous matrices, present a variety of interesting magnetic, electric and catalytic properties, that are strongly size-dependent. Among the different preparation methods which can be used to obtain this kind of materials, the sol-gel process is particularly interesting because it is affected by several parameters which allow a versatile control of the structural, textural and chemical properties of the final products. The present volume focusses on the preparation of metal-silica and metal oxide-silica (Me=Ni, Fe, Zn) nanocomposites by the sol-gel method and the characterization of their structural and magnetic properties.