Various colloidal systems including paints, printing inks, flour dough, clay paste, butters, powder bed etc. behave as substances showing very complicated mechanical properties.Their flow is non-Newtonian. Their specific viscosity-concentration relationships do not obey the Einstein law. They show thixotropy or rheopexy. Some powder systems appear as bodies showing dilatancy. Concentrated suspensions and emulsions behave as visco-elastic.The above-mentioned peculiar flow properties of colloidal suspensions and emulsions are characterized by various nonlinear nature and, from the structural point of view, formation of a scaffolding structure by the suspended or emulsified particles; the structure, which is formed by weak secondary bonds, is easily broken and regenerated in the field of flow.Some schemes of studying the complicated mechanical properties of colloidal disperse systems are discussed.One of the most classical methods of analysis is to describe their flow properties by a plastic yield value and plastic viscosity first proposed by Bingham. The concept of Bingham plasticity is conveniently applicable to the study of concentrated suspensions.Measurement of dynamic visco-elasticity of colloidal dispersions reveals the nature and the structural aspects of many rheological peculiarities. For example, spinnability or thread-forming property of some lyophile colloidal solutions is described as the superposed phenomena of viscous flow and elastic elongation.Description of their stress-strain-time behavior by the power law which was proposed by Nutting and Scott Blair makes an other way of studying rheology of pasty matters.Other schemes are of experimental nature. For example, it is recommendable to study the rheological properties of suspension of particles whose surface physico-chemical nature can be controlled by chemical treatment. Various synthetic latexes and suspensions of powders of ion-exchange resins are conveniently used as the model substances for the study of complicated rheological properties of colloids. Their surfaces are well-defined and easily controlled by chemical techniques.