This document discusses rheology modifiers, which are additives that control the flow properties of liquid formulations. It defines rheology and viscosity, and describes different types of rheology modifiers including inorganic, organic, associative, and non-associative modifiers. Quality parameters for rheology modifiers like viscosity, yield stress, and viscoelasticity are explained. Examples of specific rheology modifiers are provided like HEUR, Caesalpinia spinosa gum, and Carbomer. Methods for analyzing rheology modifiers including their structures are also summarized.