Silica-based materials are used in many high-tech products including microelectronics, optoelectronics, and catalysts. Siliceous sponges (Demospongiae and Hexactinellida) are unique in their ability to synthesize silica enzymatically. We have cloned the silica-forming enzymes, silicateins, from both demosponges (marine and freshwater sponges) and hexactinellid sponges. The recombinant enzymes allow the synthesis of silica under environmentally benign ambient conditions, while the technical (chemical) production of silica commonly requires high temperatures and pressures, and extremes of pH. Silicateins can be used for the fabrication of highly-ordered inorganic-organic composite materials with defined optical, electrical, and mechanical properties. The simple self-assembly properties of silicateins which are able to form silica and other metal oxides in aqueous solution allow the development of novel products in nano(bio)technology, medicine, and dentistry.