Clays are nanoparticles with layered structures. The layers possess net negative charge that is neutralized by cations such as Na+, K+, Ca2+, etc., which occupy the interlamellar space. The amazing amenability of clays for modification lies in the fact that these interlamellar cations can be very easily replaced by other cations or other molecules. Molecules can be covalently anchored to layer atoms. All this can be done by very simple procedures. This provides tremendous scope for altering the properties of clays like acidity, pore size, surface area, polarity and other characteristics that govern their performance as catalysts. Because of these wide ranging possibilities, in addition to their environmental compatibility and cheapness, much effort is expended in discovering newer methods of using clays in their native and modified forms as catalysts for diverse organic reactions.