Intercalation compounds of clay minerals show various properties arisen from their unique structures. The study on the clay-inorganic intercalation compounds is rapidly developing field and various synthetic methods have been proposed. New insight on the structure of the interlayer region indicates several types of interactions between silicate layers and the intercalated inorganic compounds. Clayorganic intercalation compounds can be classified into four categories. a) Organic cations can be intercalated. b) Polar organic molecules are also intercalated and the feasibility depends on the type of clay minerals. c) Clay-polymer intercalation compounds are also obtained by two different ways. d) Organic deriva-t ives are now forming a distinct area in clay-organic intercalation compounds.
The characterization techniques of clay intercalation compounds, especially recently developed instrumental analyses (Resonance Raman Spectroscopy and High Resolution Solid State NMR), are briefly described. Intercalated molecules are now well characterized and the conformation of the guest molecules can be precisely described. Their industrial applications, such as adsorbents, ion exchange materials, catalysts, dispersing agents, pigments, insulating materials, etc., are reviewed. A future prospect of the intercalation compounds is briefly described.