Hybrid Organic-Inorganic Materials: An Overview. Hybrid organic–(bio)–inorganic materials will play a major role in the development of advanced functional nanomaterials. Research in functional hybrid organic-inorganic materials is supported by the growing interest of chemists, physicists, biologists and materials scientists who are looking to fully exploit this opportunity for creating smart materials that benefit from the best of the three realms: inorganic, organic and biological… …Hybrid organic–inorganic materials are not simply physical mixtures. They can be broadly defined as molecular or nano-composites with organic (or bio) and inorganic components, intimately mixed where at least one of the component domains has a dimension ranging from a few Å to several nanometers. Consequently the properties of hybrid materials are not only the sum of the individual contributions of both phases, but the role of their inner interfaces could be predominant. The nature of the interface has been used to grossly divide these materials into two distinct classes: (Sanchez 1994 New Journal of Chemistry) In Class I, organic and inorganic components are embedded and only hydrogen, van der Waals or ionic bonds give cohesion to the whole structure. In Class II materials, the two phases are partly linked together through strong chemical covalent or iono-covalent bonds. Molecular approaches of molecular and solid state chemistry and nanochemistry have reached a very high level of sophistication. Chemists can tailormake many molecular species and design new functional hybrid materials with enhanced properties. Indeed, numerous hybrid materials are synthesised and processed by using soft chemistry routes based on: • the polymerisation of functional organosilanes, macromonomers and metallic alkoxides; • the encapsulation of organic components within sol–gel derived organosilicas or hybrid metallic oxides; • the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures; • self-assembly or templated growth, nano-building block approaches, hydrothermally processed hybrid zeolites or microporous metal organic frameworks, integrative synthesis or coupled processes, bio-inspired strategies, etc… …Organic–inorganic hybrid materials do not only represent a creative alternative for the design of new materials and compounds for academic research, but their improved or unusual features open promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology and medicine. Applications include smart membranes and separation devices, functional smart coatings, a new generation of photovoltaic and fuel cells, photocatalysts, new catalysts, sensors, smart microelectronics, micro-optical and photonic components and systems for nanophotonics, innovative cosmetics, intelligent therapeutic vectors that combine targeting, imaging, therapy and controlled release of active molecules, nanoceramic–polymer composites for the automobile or packaging industries, etc… …Today, this potential is becoming reality. Indeed many of these hybrid materials are entering niche markets that should expand in the future because new and stricter requirements are now being set up to achieve greater harmony between the environment and human activities. New materials and systems produced by man must in the future aim at higher levels of sophistication and miniaturisation. They must respect the environment and consume less energy with features such as recyclability and reliability. It is just a question of scientists’ imagination and of making industry aware of their opportunities and benefits… For more information about Hybrid Organic-Inorganic Materials, see for example the following documents: Journal of Materials Chemistry, 2005, volume 15, Issue 35-36, Pages 3541-3988. (Impact Factor: 4,287). Theme issue: Functional Hybrid Materials. Guest editor: Clément Sanchez. Functional Hybrid Materials, Pedro Gómez-Romero / Clément Sanchez (eds.), 2003, Wiley-VCH, ISBN-10: 3-527-30484-3. Hybrid Materials, Guido Kickelbick (ed.), 2006, Wiley-VCH, ISBN-10: 3-527-31299-4. MRS Symposium Proceedings Organic/Inorganic Hybrid Materials. Volumes 435, 519, 576, 628; 726, 847.