The objective of this paper is to give an overview of the colloidal properties of clays and to describe the work performed until the present moment in the area of adsorption of non-ionic polymers onto clay and the rheology of clay suspensions. The review is particularly focused on Na+-montmorillonite clay of the smectite group (Bentonite), due to its high swelling capacity, the ability to adsorb significant amounts of polymer on its surfaces, and the formation of a gel-like structure with yield characteristics and viscoelastic properties at relatively low clay concentrations. A significant amount of research has been performed in these areas with applicability to various fields, such as soil science and drilling fluids, where interaction of organic polymers with the clay surface and the rheological response in the presence of electrolytes under different temperature and pressure conditions are of considerable relevance. In order to understand the interaction of these compounds with the clay surface and the rheological response of the resulting suspensions, it becomes essential to understand the structure of clay minerals, the interaction of clay particles in aqueous medium, the swelling behaviour and electrokinetic properties of Na+-montmorillonite clay. For this reason, the above topics are addressed, along with the general features of stabilisation of colloidal particles and the adsorption mechanism of non-ionic compounds on hydrophilic surfaces. A comprehensive review of the most relevant studies of the adsorption of non-ionic surfactants and polymers onto both silica and clay is presented. Finally, an overview of the rheological behaviour of concentrated suspensions and models used to describe the flow behaviour of clay suspensions is given, along with the effect of electrolytes, polymers, high pressure and high temperature on the flow behaviour of Na+-montmorillonite suspensions.