This chapter discusses the performance and applications of pharmaceutical polymers in relation to their structure and degree of disorder. It first gives an overview of the main characteristics of polymers in terms of their architecture, physical states, and mobility. The chapter highlights the different origins and types of disorders that can be found in polymers, namely structural disorders and dynamic disorders. Pharmaceutical polymers are widely used in solid dosage forms such as drug/excipient amorphous solid dispersions, which are mixtures of polymers and low molecular weight (MW) drugs. The chapter particularly focuses on the influence of drug incorporation on the polymer mobility and the issues of the limits of polymer-drug miscibility and solubility. Finally, it discusses the relationship between the disorder and the physical properties and behavior of pharmaceutical polymers when used in solid dosage forms through a few illustrative examples involving the most widely used polymers.