The author adopts the original Freundlich-Peterfi definition of thixotropy, that is the reversible isothermal gel/sol/gel/transformation induced by shear and subsequent rest. The criterion of a gel is the presence of a “Yield Value”, and that of a sol the absence of a “Yield Value”. It is recognised, that most of Freundlich's “thixotropic” systems did not conform to this definition; rather they were gels which became less viscous on shearing but never became true sols: such systems the author describes as “false-body” systems. The author briefly describes his electromagnetic thixotrometer, the “constant reading viscometer”, and the “twin-Couette” viscometer, and illustrates their application to the study of the influence of the rate of shear, the measurement of “Yield Value”, the influence of the concentration of solid and the effects of the “dispersion power” of the liquid. Figures are shown of curves of “elastic recoil” in such systems as heather honey, mayonnaise, cream, paints and bentonite suspensions; and the applications of “elastic recoil” to the study of structural viscosity. Illustrations are given of the different Theological states obtained by dispersing fine particles in Newtonian liquids and in non-Newtonian fluids. A range of curves illustrates the variations in the effects of time on different types of colloidal systems; and it is shown how these curves can be applied to predict the behaviour of such systems over long periods of time. Finally a generalised diagram is used to show how the degree of dispersion can be determined from the rheological state of a colloidal system; and it is shown that dispersion increases as we pass along the rheological states: Structural viscosity — false-body — thixotropy —dilatancy — Newtonian flow.