Clay minerals interact with organic materials by adsorption, intercalation and cation exchange. Basic principles of intercalation reactions were obtained with kaolinite which intercalates a limited number of neutral organic compounds. The interaction of neutral organic compounds with mica-type layer silicates (2/1 clay minerals) is of quite different type. As illustrated for the interaction with nuclein bases, the adsorption can be strikingly dependent on the layer charge and the concentration of salts and co-adsorption phenomena can occur. Various organic materials are bound by cation exchange. Besides some other examples, the reaction with alkylammonium ions is of interest because of widespread practical applications. From a more scientific point of view, the interactions of alkylammonium ions with clays provide models for studying surfactant aggregations on solid surfaces and possible conformational changes in aggregates of long chain compounds (mono- and bimolecular films, as in biomembranes). Negatively charged organic ions can also be bound by clays. The main mechanisms are binding by positive edge charges or exchanging structural OH-groups.