The sol-gel polycondensation of alkoxysilanes has been recently used for the preparation of silicate materials called CERAMERs or ORMSILs which found application in the production of various ceramic and glass products for various fields. The reaction mechanism of the whole sol-gel process has to be understood because properties of the products closely depend on the process of formation and reaction conditions. The knowledge of kinetics and mechanism of the acid- and base-catalyzed hydrolysis and condensation is surveyed. The formation of basic building units, their subsequent aggregation, formation and development of gel, gel structure, and chemical composition in the gel point, and changes in the structure of siloxane network during drying are discussed. Some physical properties of gels and siloxane materials are compared as they depend of the conditions of sol-gel process.