Clay suspensions and coloidal systems in general. Properties of hydrophobic sols. The theory of the stability of hydrophobic sols. Succees of the theory of stability further theories and refinements. Clay mineralogy. Praticle size and shape, surfaca area, and density of charge. Electric double-layer structure and stability of clay suspensions. Peptization of clay suspensions. Technological applications of stability contorl, sedimentation, filtration, and flow behavior. Interlamellar and osmotic swelling application. Interaction of clays and organic compounds. Electrokinetic and electrochemical properties of clay water systems. Note on the preparation of clay suspensions. Electric double-layer computation. Miscellaneous computer data for montmorillonites. Van der waals attraction energy between two layers.