This chapter deals with some of the background to the water-soluble synthetic polymers, before proceeding to consider the properties and behavior of the specific polymers. Many of the water-soluble polymers have medical and pharmaceutical applications, and this area has been cataloged, reviewed, and discussed. The chapter looks at some useful comparisons between the features of the synthetic water-soluble polymers and those of the natural and the semisynthetic types. The modified natural polymers comprise mainly the diverse derivatives of cellulose. One apparent advantage in studying the commercial grades of these polymers is that the results should presumably be directly applicable to the actual use of the material. Many of these polymers are hygroscopic, and the determination of the water content of the bulk polymer is therefore a perennial problem. From the practical viewpoint, one of the most useful features of polymers is their ability to increase the viscosity of a liquid in which they are dissolved, even at low concentrations.