The sol-gel method is firstly described taking the TiO2-SiO2system as an example of the chemical procedure and its effect on the structure of the obtained material. The possibilities given by this low temperature synthesis are briefly described giving particular emphasis on so-called hybrid materials. The second part of the paper is devoted to defects in sol-gel materials. Studies on Raman active defects and paramagnetic states are reviewed. A brief discussion on crystallization defects is also presented.